The layer of cells lining the outer surface of the mammalian ovary, the ovarian surface epithelium (OSE), is a constant feature throughout the dynamic tissue remodeling that occurs throughout the reproductive cycle (follicle growth, ovulation, corpora lutea formation and pregnancy). Abnormal development of these cells is responsible for 90% of all epithelial ovarian cancers in women and epidemiological studies have shown that susceptibility to ovarian cancer is negatively correlated with increasing pregnancy. Little is known about how OSE cells are affected at each stage of the cycle, so the main aim of this study was to determine how the reproductive cycle affected proliferation and degeneration of OSE cells. This study utilised three animal models each with a different type of reproductive cycle: a mono-ovular seasonal breeder (Sheep), a mono-ovular polyoestrous breeder (Cow) and a poly-ovular non human primate (marmoset) to allow comparisons to be made. Comparison of OSE proliferative activity was made in sheep and marmoset at each stage of the cycle including pregnancy and anoestrous. The bovine model was used to investigate apoptotic cell death. Proliferative activity of somatic cells within the sheep ovary was monitored throughout the reproductive cycle by detection of cell cycle markers PCNA and Ki67 using immunohistochemistry. The pattern of OSE proliferation was correlated with the pattern of follicle development at each stage (sheep and marmoset). During pregnancy cell proliferation was significantly lower in OSE and in granulosa cells, reflecting a suppression of mature follicle development during these stages whereas in cycling animals proliferation was increased. Differences in OSE proliferation were observed in relation to the local underlying tissue environment in both sheep and marmoset. Epithelial cell rupture and regeneration enhanced the hormonal mitogenic action on epithelial cells, which showed highest proliferation over corpora lutea in each animal model. To test the hypothesis that these changes are mediated by hormones or growth factors ovine OSE cells were cultured and proliferative activity monitored after treatment with several factors: fetal calf serum (FCS), follicular fluid from follicles of varying sizes, corpora lutea extracts, recombinant human IGF-1, oestradiol and progesterone. IGF alone was demonstrated to have an affect on increasing proliferation of cultured OSE cells. Levels of FSHr and LHr were monitored by quantitative real- time PCR and it was demonstrated that the concentration of gonadotrophin receptors in OSE, increased prior to and after ovulation, at which time the in vivo OSE proliferation also peaked. The in situ apoptosis index was determined in bovine tissue using TUNEL throughout the regular cycle, and at mid and late-pregnancy stages. The results showed that pregnancy induced apoptotic activity in OSE cells and up regulated the tumour suppressor gene p53. Cultured bovine OSE cells also exhibited an increased level of apoptosis following progesterone treatment. Since p53/p53 gene expression in OSE over the corpora lutea producing progesterone also increased, this progesterone-mediated apoptosis may be mediated through an up-regulation of p53 synthesis. The effect of pregnancy and low production of gonadotrophins in the regulation of OSE cell morphology and activity was further investigated in the marmoset monkey (a non-human primate) treated with GnRH antagonist and infused with BrdU to monitor proliferative activity. OSE proliferation was correlated to ovarian events (follicular growth, ovulation and luteinization) and this was suppressed during pregnancy. Inhibition of gonadotrophin secretion by treatment with a GnRH antagonist also markedly inhibited OSE proliferation. Taken together these studies support the hypothesis that pregnancy and periods of anovulation reduce proliferation of OSE cells and alter the pattern of apoptotic cell death and that this effect is independent of species and reproductive pattern. Suppression of gonadotrophins and other growth factors during pregnancy could enhance p53-mediated apoptosis of damaged and mitogenic cells arising from repeated ovulations. This effect may partly explain why increasing number of pregnancies in woman reduces the chance of epithelial ovarian cancers.

No description available.

Low recruitment is the largest challenge facing the recovery of the critically endangered Mississippi Sandhill Crane (Grus canadensis pulla). Lack of information on sources of nest failure hinders effective management to increase recruitment. I examined sources of nest failure for 54 nests at the Mississippi Sandhill Crane National Wildlife Refuge, 2008-2009. Nest cameras identified predation as the primary source of failure, followed by flooding, abandonment, and egg inviability. Mean daily survival rate (DSR) was 0.72. The best approximating models included covariates for season date, temperature and nest age. DSR decreased with increasing season date, increasing nest age, and decreasing temperature. Hypotheses related to effects of renesting, human disturbance, precipitation, flooding, and winter rain were not supported. Because predation has been identified as a primary source of nest failure, I also monitored mammalian predators on the MSCNWR. Coyotes and raccoons were most common, with gray foxes, red foxes, domestic dogs, and bobcats also detected frequently.

Thesis advisor: Mary F. Roberts / Thesis advisor: Eranthie Weerapana / Peripheral proteins from mammals often exhibit multi-domain structures and require metal ions such as calcium as co-factors. This dissertation investigates two types of such proteins -- pulmonary collectins (surfactant proteins A and D) and phosphatidylinositol-specific phospholipase C (PLC) delta1 -- and their interactions with model membranes. One approach to work around the complexity brought upon by such multi-domain protein structure is to use a truncated construct or an isolated single domain. For pulmonary collectins, homotrimers consisting of the neck domain and the carbohydrate recognition domain were used in a novel NMR assay for better understanding of their lipid-specific interactions with the membranes. For PLC delta1, we were particularly interested in the role of the EF-hand domain. The isolated EF-hand domain of PLC delta1 was first used to characterize its interactions with membranes and identify key residues responsible for such interactions. These key residues in the N terminal lobe of the EF-hand domain, either cationic or hydrophobic, were then found to affect the hydrolysis activity of the full-length enzyme. A common role for this region of the PLC in facilitating proper membrane association was thus proposed. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

O DNA está constantemente exposto a danos causados tanto por agentes endógenos quanto exógenos. Estes podem causar diferentes tipos de lesões incluindo modificações de bases e do açúcar, além de quebras de fitas simples ou duplas. As quebras de duplas fitas, quando comparadas às demais, constituem as mais citotóxicas e podem resultar em deleções no DNA e instabilidade genética. Deleções no DNA mitocondrial (mtDNA) causam diversas doenças e estão envolvidas no processo de envelhecimento. No núcleo, as quebras de duplas fitas no DNA podem ser reparadas por recombinação homóloga (HR), ligação de pontas não homólogas (NHEJ) e anelamento de fita simples (SSA). No entanto, em mitocôndrias de células de mamíferos, o reparo de quebras de duplas fitas ainda não foi completamente caracterizado. Experimentos in vitro usando extratos mitocondriais de células de roedores mostraram que estes são capazes de reparar essas quebras, no entanto pouco é sabido sobre quais proteínas são responsáveis por cada etapa de reparo, bem como sua implicação na manutenção da integridade do genoma mitocondrial. Sendo assim, nesse trabalho investigamos a localização e função mitocondrial das proteínas ATM, Rad51, Rad52, Ku70/86 e DNA-PKCs, que são sabidamente envolvidas em reparo de quebras de duplas fitas no núcleo. Para identificar essas proteínas em mitocôndrias de células de mamíferos, mitocôndrias foram isoladas a partir de células da linhagem HEK293T, usando centrifugação diferencial seguida por gradiente de Percoll. Para as proteínas de recombinação homóloga, ATM e Rad51, imunodetectamos isoformas semelhantes em todos os compartimentos celulares. Já para a proteína Rad52 o mesmo anticorpo imunodetectou duas bandas distintas na mitocôndria ao passo que no núcleo foram quatro. Além disso, verificamos que baixos níveis de proteína Rad52, induzidos pela expressão de shRNA (short hairping RNA) específico, resultam em diminuição do número de cópias de mtDNA bem como acúmulo de deleções no genoma mitocondrial. Para as proteínas de NHEJ, DNA-PKCs e a subunidade Ku70, identificamos isoformas semelhantes em todos os compartimentos celulares. Já para a subunidade 86 do heterodímero Ku70/86 o anticorpo detectou, somente em mitocôndrias, uma banda menor de 50 kDa, a qual difere na região N-terminal da subunidade detectada no núcleo (86 KDa). Experimentos de co-imunprecitação de proteínas mostraram que essa isoforma menor compõe o heterodímero mitocondrial juntamente com a subunidade 70 (mtKu70/50) e que esse interage com DNA ligase III mitocondrial. Nossos resultados também mostraram que a estabilidade proteica de mtKu70/50 é regulada por ATM. Tratamento das células com peróxido de hidrogênio, que induz quebras de duplas fitas, aumentou a associação do heterodímero mtKu70/50 com o mtDNA, de forma independente de aumento da concentração proteica intra-mitocondrial. Já a diminuição dos níveis proteicos de Ku, induzida através de shRNA, resultou em diminuição do número de cópias de mtDNA e acumulo de danos nesse genoma. Extratos mitocondriais de células knockdown para Ku apresentaram menor atividade de reparo NHEJ em um ensaio in vitro, sugerindo que o acúmulo de danos nestas células é provavelmente devido a deficiências na via de NHEJ. Em conjunto, nossos dados sugerem que tanto HR quanto NHEJ operam em mitocôndrias. Além disso, a via de NHEJ mitocondrial utiliza o heterodímero mitocondrial Ku70/50 o qual está envolvido na manutenção do mtDNA. Ademais, nossos resultados mostram uma grande conservação molecular e funcional entre as vias de reparo de NHEJ e HR no núcleo e na mitocôndria, o que reforça sua importância para a manutenção da estabilidade genômica mitocondrial e, provavelmente a função mitocondrial. / DNA is constantly exposed to damaging agents from both endogenous and exogenous sources. These can cause different types of DNA lesions that include base and sugar modifications and single and double strand breaks. DNA doublestrand breaks (DSBs) are among the most cytotoxic DNA lesions, which can result in deletions and genetic instability. Deletions in the mitochondrial DNA (mtDNA) cause numerous human diseases and drive normal aging. DSBs in the nuclear DNA are repaired by non-homologous DNA end joining (NHEJ), homologous recombination (HR) or Single Strand Annealing (SSA). Yet, repair of DSBs in mammalian mitochondria has not been fully characterized. Mitochondrial extracts from rodent cells are proficient in ligating DNA ends in vitro, but little is known about which proteins are responsible for each enzymatic step and its implication in mitochondrial genome maintenance. Thus, we investigated mitochondrial localization and function of DSBR (double strand break repair) proteins ATM, Rad51, Rad52, the Ku70/86 heterodimer and DNA-PKCs.To identify DSBR proteins in mammalian mitochondria, highly purified mitochondria from HEK293T cells were isolated using differential centrifugation followed by Percoll gradient. For HR proteins, we detected similar isoforms for ATM and Rad51 proteins in all cellular compartments. Two mitochondriaspecific isoforms of Rad52 were detected, while the same antibody detected four isoforms in the nucleus. In addition, lower Rad52 protein levels, induced by specific shRNA expression, result in decreased mtDNA copy number and accumulation of deleted mitochondrial genomes. For NHEJ proteins, similar isoforms of DNA-PKcs and the Ku70 subunit were detected in all cellular compartments. On the other hand, antibodies against the Ku86 subunit detected a smaller band in mitochondrial extracts (50 KDa), lacking the N-terminal region of the canonical isoform detected in the nucleus (86 KDa). The mitochondrial Ku70/50 heterodimer interacts with mitochondrial DNA ligase III, suggesting a role in DSBR. Moreover, stability of the mtKu heterodimer is regulated by ATM. Hydrogen peroxide treatment, which induces DSBs, increases mtKu70/50 association with the mtDNA and cells with reduced Ku levels, also induced by shRNA transfection, have lower mtDNA copy number and accumulate mtDNA damage. Moreover, mitochondrial extracts from Ku knockdown cells show lower NHEJ repair activity in an in vitro assay, suggesting that damage accumulation in these cells is likely due to deficiencies in NHEJ. Together, our data suggest that both HR and NHEJ operate in mitochondria. Also, mtNHEJ requires the Ku heterodimer and is involved in mtDNA maintenance. Moreover, our results indicate that there is a significant molecular and functional conservation between NHEJ and HR repair pathways in the nucleus and in mitochondria, which reinforces their importance for maintenance of mitochondrial genomic stability and, likely mitochondrial function.

The mammalian target of rapamycin (mTOR) signalling pathway takes part in both extracellular and intracellular signals. It is a major regulator of cell metabolism, growth, proliferation and survival. mTOR also regulates critical processes such as cytoskeletal organization, ribosomal biogenesis, transcription and protein synthesis. The mTOR pathway has been implicated in many diseases such as cancer, neurodegeneration and diabetes, which impact homeostasis and cellular functions. Moreover, mTOR has also been shown to play a critical role in immune cell regulation of T and B cells together with neutrophils and antigen presenting cells, as it integrates signals between them extending to the entire immune microenvironment. The aim of my study was to investigate the role of a component of the mTOR complex 1, Raptor, in myeloid cells. My findings show that the absence of Raptor knock out (KO) does not affect bone marrow derived macrophage (BMDM) differentiation and maturation. However, the absence of Raptor influences BMDM polarisation towards an inflammatory phenotype, at least at the level of transcription as observed by increases in mRNA expression of inflammatory cytokines such as TNFα, IL-12β, and IL-6. This finding was consolidated by an increase in NFκΒ pathway signalling in Raptor KO BMDMs. Downstream intracellular signalling in myeloid cells was affected by deletion of Raptor as I found reduced S6K phosphorylation in Raptor KO BMDMs compared to wild type (WT) BMDMs. As a consequence of Raptor absence in BMDMs, STAT3 phosphorylation was also reduced. Raptor deletion did not impact the PI3K/Akt signalling pathway, but decreased phosphorylation of ERK. BMDMs lacking Raptor had reduced phagocytic activity as they were also observed to migrate less towards a pancreatic cancer cell line. However preliminary experiments in pancreatic cancer models did not indicate a major role for Raptor in the activity of tumour associated myeloid cells. My results demonstrate that Raptor and by implication mTORC1, is involved in macrophage polarisation and function.

O DNA está constantemente exposto a danos causados tanto por agentes endógenos quanto exógenos. Estes podem causar diferentes tipos de lesões incluindo modificações de bases e do açúcar, além de quebras de fitas simples ou duplas. As quebras de duplas fitas, quando comparadas às demais, constituem as mais citotóxicas e podem resultar em deleções no DNA e instabilidade genética. Deleções no DNA mitocondrial (mtDNA) causam diversas doenças e estão envolvidas no processo de envelhecimento. No núcleo, as quebras de duplas fitas no DNA podem ser reparadas por recombinação homóloga (HR), ligação de pontas não homólogas (NHEJ) e anelamento de fita simples (SSA). No entanto, em mitocôndrias de células de mamíferos, o reparo de quebras de duplas fitas ainda não foi completamente caracterizado. Experimentos in vitro usando extratos mitocondriais de células de roedores mostraram que estes são capazes de reparar essas quebras, no entanto pouco é sabido sobre quais proteínas são responsáveis por cada etapa de reparo, bem como sua implicação na manutenção da integridade do genoma mitocondrial. Sendo assim, nesse trabalho investigamos a localização e função mitocondrial das proteínas ATM, Rad51, Rad52, Ku70/86 e DNA-PKCs, que são sabidamente envolvidas em reparo de quebras de duplas fitas no núcleo. Para identificar essas proteínas em mitocôndrias de células de mamíferos, mitocôndrias foram isoladas a partir de células da linhagem HEK293T, usando centrifugação diferencial seguida por gradiente de Percoll. Para as proteínas de recombinação homóloga, ATM e Rad51, imunodetectamos isoformas semelhantes em todos os compartimentos celulares. Já para a proteína Rad52 o mesmo anticorpo imunodetectou duas bandas distintas na mitocôndria ao passo que no núcleo foram quatro. Além disso, verificamos que baixos níveis de proteína Rad52, induzidos pela expressão de shRNA (short hairping RNA) específico, resultam em diminuição do número de cópias de mtDNA bem como acúmulo de deleções no genoma mitocondrial. Para as proteínas de NHEJ, DNA-PKCs e a subunidade Ku70, identificamos isoformas semelhantes em todos os compartimentos celulares. Já para a subunidade 86 do heterodímero Ku70/86 o anticorpo detectou, somente em mitocôndrias, uma banda menor de 50 kDa, a qual difere na região N-terminal da subunidade detectada no núcleo (86 KDa). Experimentos de co-imunprecitação de proteínas mostraram que essa isoforma menor compõe o heterodímero mitocondrial juntamente com a subunidade 70 (mtKu70/50) e que esse interage com DNA ligase III mitocondrial. Nossos resultados também mostraram que a estabilidade proteica de mtKu70/50 é regulada por ATM. Tratamento das células com peróxido de hidrogênio, que induz quebras de duplas fitas, aumentou a associação do heterodímero mtKu70/50 com o mtDNA, de forma independente de aumento da concentração proteica intra-mitocondrial. Já a diminuição dos níveis proteicos de Ku, induzida através de shRNA, resultou em diminuição do número de cópias de mtDNA e acumulo de danos nesse genoma. Extratos mitocondriais de células knockdown para Ku apresentaram menor atividade de reparo NHEJ em um ensaio in vitro, sugerindo que o acúmulo de danos nestas células é provavelmente devido a deficiências na via de NHEJ. Em conjunto, nossos dados sugerem que tanto HR quanto NHEJ operam em mitocôndrias. Além disso, a via de NHEJ mitocondrial utiliza o heterodímero mitocondrial Ku70/50 o qual está envolvido na manutenção do mtDNA. Ademais, nossos resultados mostram uma grande conservação molecular e funcional entre as vias de reparo de NHEJ e HR no núcleo e na mitocôndria, o que reforça sua importância para a manutenção da estabilidade genômica mitocondrial e, provavelmente a função mitocondrial. / DNA is constantly exposed to damaging agents from both endogenous and exogenous sources. These can cause different types of DNA lesions that include base and sugar modifications and single and double strand breaks. DNA doublestrand breaks (DSBs) are among the most cytotoxic DNA lesions, which can result in deletions and genetic instability. Deletions in the mitochondrial DNA (mtDNA) cause numerous human diseases and drive normal aging. DSBs in the nuclear DNA are repaired by non-homologous DNA end joining (NHEJ), homologous recombination (HR) or Single Strand Annealing (SSA). Yet, repair of DSBs in mammalian mitochondria has not been fully characterized. Mitochondrial extracts from rodent cells are proficient in ligating DNA ends in vitro, but little is known about which proteins are responsible for each enzymatic step and its implication in mitochondrial genome maintenance. Thus, we investigated mitochondrial localization and function of DSBR (double strand break repair) proteins ATM, Rad51, Rad52, the Ku70/86 heterodimer and DNA-PKCs.To identify DSBR proteins in mammalian mitochondria, highly purified mitochondria from HEK293T cells were isolated using differential centrifugation followed by Percoll gradient. For HR proteins, we detected similar isoforms for ATM and Rad51 proteins in all cellular compartments. Two mitochondriaspecific isoforms of Rad52 were detected, while the same antibody detected four isoforms in the nucleus. In addition, lower Rad52 protein levels, induced by specific shRNA expression, result in decreased mtDNA copy number and accumulation of deleted mitochondrial genomes. For NHEJ proteins, similar isoforms of DNA-PKcs and the Ku70 subunit were detected in all cellular compartments. On the other hand, antibodies against the Ku86 subunit detected a smaller band in mitochondrial extracts (50 KDa), lacking the N-terminal region of the canonical isoform detected in the nucleus (86 KDa). The mitochondrial Ku70/50 heterodimer interacts with mitochondrial DNA ligase III, suggesting a role in DSBR. Moreover, stability of the mtKu heterodimer is regulated by ATM. Hydrogen peroxide treatment, which induces DSBs, increases mtKu70/50 association with the mtDNA and cells with reduced Ku levels, also induced by shRNA transfection, have lower mtDNA copy number and accumulate mtDNA damage. Moreover, mitochondrial extracts from Ku knockdown cells show lower NHEJ repair activity in an in vitro assay, suggesting that damage accumulation in these cells is likely due to deficiencies in NHEJ. Together, our data suggest that both HR and NHEJ operate in mitochondria. Also, mtNHEJ requires the Ku heterodimer and is involved in mtDNA maintenance. Moreover, our results indicate that there is a significant molecular and functional conservation between NHEJ and HR repair pathways in the nucleus and in mitochondria, which reinforces their importance for maintenance of mitochondrial genomic stability and, likely mitochondrial function.

Mitochondria are a key organelle within human cells, with functions ranging from ATP synthesis to apoptosis. Changes in mitochondrial function are associated with many diseases, as well as 'natural' processes like ageing. Mitochondria have a unique evolutionary origin, as the result of an endosymbiotic relationship between a bacterium and an archaeal cell. Therefore, the phylogenetic history of the mitochondrial proteome is also unique within the total human proteome. A new description of the genes encoding the human mitochondrial proteome - IMPI (Integrated Mitochondrial Protein Index) 2017 - provided an opportunity for exploration of mitochondrial proteome history and the application of this knowledge to the understanding of gene function, disease and ageing. To facilitate the exploration of the mitochondrial proteome, I created a manually curated dataset of 190,097 predicted orthologues of the 1,550 IMPI 2017 human genes across 359 species, using reciprocal best hit analysis as the basis for orthologue prediction. I used this to explore gene history and the potential for phylogenetic profiling to predict the function of uncharacterised genes. This inspired the use of phylogenetic profiling within two phyla of animals, to link presence and absence of metabolic genes to the function of mitochondrial transporters. Potential transport substrates were predicted for two groups of uncharacterised mitochondrial carriers. I also used the dataset to identify features of genes associated with monogenetic disease, as well as differences between recessive and dominant disease genes. A similar orthologue identification method was used to explore the total sequenced viral proteome for potential orthologues of mitochondrial proteins. This showed that a range of mitochondrial proteins are shared with viruses, potentially facilitating the co-opting of mitochondrial function during viral infection of eukaryotic cells. I then used orthology to explore the conservation of residues linked to protein acetylation and identify a link with lifespan in warm-blooded vertebrates. In conclusion, I have used orthology to further the understanding of human mitochondrial proteome history and developed applications of this information. For example, phylogenetic features of disease genes are being used as part of a wider pipeline to predict mitochondrial disease genes. Furthermore, predicted substrates of the SLC25A14/30 mitochondrial carriers are being tested. My dataset provides further opportunities to explore the evolution and function of the mitochondrion.

abstract: Chromatin is the dynamic structure of proteins and nucleic acids into which eukaryotic genomes are organized. For those looking to engineer mammalian genomes, chromatin is both an opportunity and an obstacle. While chromatin provides another tool with which to control gene expression, regional density can lead to variability in genome editing efficiency by CRISPR/Cas9 systems. Many groups have attempted to de-silence chromatin to regulate genes and enhance DNA's accessibility to nucleases, but inconsistent results leave outstanding questions. Here, I test different types of activators, to analyze changes in chromatin features that result for chromatin opening, and to identify the critical biochemical features that support artificially generated open, transcriptionally active chromatin. I designed, built, and tested a panel of synthetic pioneer factors (SPiFs) to open condensed, repressive chromatin with the aims of 1) activating repressed transgenes in mammalian cells and 2) reversing the inhibitory effects of closed chromatin on Cas9-endonuclease activity. Pioneer factors are unique in their ability to bind DNA in closed chromatin. In order to repurpose this natural function, I designed SPiFs from a Gal4 DNA binding domain, which has inherent pioneer functionality, fused with chromatin-modifying peptides with distinct functions. SPiFs with transcriptional activation as their primary mechanism were able to reverse this repression and induced a stably active state. My work also revealed the active site from proto-oncogene MYB as a novel transgene activator. To determine if MYB could be used generally to restore transgene expression, I fused it to a deactivated Cas9 and targeted a silenced transgene in native heterochromatin. The resulting activator was able to reverse silencing and can be chemically controlled with a small molecule drug. Other SPiFs in my panel did not increase gene expression. However, pretreatment with several of these expression-neutral SPiFs increased Cas9-mediated editing in closed chromatin, suggesting a crucial difference between chromatin that is accessible and that which contains genes being actively transcribed. Understanding this distinction will be vital to the engineering of stable transgenic cell lines for product production and disease modeling, as well as therapeutic applications such as restoring epigenetic order to misregulated disease cells. / Dissertation/Thesis / Doctoral Dissertation Biological Design 2019

It has been shown in previous studies that when sulfite is absorbed by rabbits via either inhalation of SO2 or oral exposure to sulfite, the hydrated form, bisulfite, interacts with plasma disulfides where it is suspected to be in the form, cysteine-S-sulfonate. A rapid and specific gas chromatographic analysis procedure for cysteine-S-sulfonate has been developed to better study the distribution of sulfite in biological systems. Sulfonated proteins are enzymatically hydrolyzed to ensure stability of the acid labile S-sulfonate disulfide. The hydrolysate is then applied to a 6 cm cation-exchange column and eluted with 0.1 N HCl which elutes the acidic cysteine-S-sulfonate with the void volume of the column leaving behind any remaining cysteine. the silylated derivatives of the column effluent are prepared using Tri-Sil/BSA. These derivatives are injected into a gas chromatograph equipped with a flame-photometric detector operating in the sulfur mode, 2% 0v-101 on Chromosorb W/HP 1/4 inch glass column, oven temperture 140°C, and carrier flow rate of 86 ml/min. The presence of cysteine-S-sulfonat in the sulfite treated rabbits had been directly determined by the described method.