Recent investigations suggest that reducing stearoyl CoA desaturase (SCD) 1 expression confers protection against obesity and insulin resistance, whereas others show that increasing SCD1 expression protects cells from lipotoxicity. The overall aim of this thesis was to establish the role of SCD1 expression in fatty acid metabolism and insulin stimulated glucose disposal in skeletal muscle. In vitro and in vivo studies were conducted to investigate the relationship between fatty acid subtype, SCD1 expression and fuel metabolism. The role of fatty acid subtype on fatty acid metabolite accumulation and insulin resistance was initially examined in rats. Rats were provided with a low fat diet or a high fat diet consisting of predominantly saturated (SAT) or polyunsaturated fatty acids (PUFA). Rats fed a SAT diet were insulin resistant and had increased skeletal muscle diacylglycerol content whereas rats fed a PUFA diet retained insulin sensitivity and accumulated triacylglycerol rather than diacylglycerol. Interestingly, SCD1 mRNA and protein content were elevated in SAT rats compared with PUFA fed and control fed rats, indicating a possible involvement of SCD1 in the aetiology of insulin resistance. Subsequently, SCD1 expression was examined in the skeletal muscle of various rodent models of genetic and diet-induced obesity. SCD1 content was consistently upregulated in the skeletal muscle of obese rodents. To determine whether SCD1 contributes to or protects from fatty-acid induced insulin resistance, SCD1 levels were transiently altered in L6 skeletal muscle myotubes. Short interfering (si) RNA was used to decrease SCD1 content and a pcDNA3.1/HygromSCD1 vector was introduced to increase SCD1 content. Reducing SCD1 protein resulted in marked esterification of exogenous fatty acids into diacylglycerol and ceramide. Insulin-stimulated Akt (acute transforming retrovirus thymoma) phosphorylation and 2-deoxyglucose uptake were reduced with SCD1 siRNA. Exposure of L6 myotubes to palmitate abolished insulin-stimulated glucose uptake in both control and SCD1 siRNA myotubes. Transient overexpression of SCD1 resulted in triacylglycerol esterification but attenuated ceramide and diacylglycerol accumulation and protected myotubes from fatty acid-induced insulin resistance. Further, these changes were associated with reduced phosphorylation of c-Jun Amino-Terminal Kinase (JNK) and the inhibitor of IêB kinase (IKK), both of which impair insulin signalling. These studies indicated that SCD1 protects from cellular toxicity in L6 myotubes by preventing excessive accumulation of bioactive lipid metabolites. Collectively, these experiments indicate that increasing SCD1 expression may be a protective mechanism designed to prevent insulin resistance in obese phenotypes.

[N,N??-bis-(mercaptoethyl)-1,5-diazacyclooctanato]NiII, Ni-1, is known to undergo metallation reactions with numerous metals. [N,N??-bis-(mercaptoethyl)-1,5-diazacycloheptanato]NiII, (bme-dach)Ni or Ni-1??, differs from Ni-1 by one less carbon in its diazacycle backbone ring producing subtle differences in N2S2Ni geometry. Metallation of Ni-1?? with PdCl2, Pd(NO3)2, and NiBr2 produced three structural forms: Ni2Pd basket, Ni4Pd2 C4-paddlewheel, and Ni3 slant chair. In attempts to provide a rationale for the heterogeneity in the active site of Acetyl coA Synthase, metal ion capture studies of Ni-1 in methanol found a qualitative ranking of metal ion preference: Zn2+ < Ni2+ < Cu+. Formation constants for metal ion capture of Ni-1?? in water were determined for Pb2+, Ni2+, Zn2+, Cu+, and Ag+. A quantitative estimate places copper some 15 orders of magnitude above nickel or zinc in binding affinity. Sulfur dioxide uptake by Ni-1?? is characterized by significant color change, improved adduct solubility, and reversible binding of two equivalents of SO2. These combined properties establish Ni-1?? as a suitable model for gas uptake at nickel thiolate sites and as a possibly useful chemical sensor for this poisonous gas. Comparisons of molecular structures, ν(SO) stretching frequencies, and thermal gravimetric analyses are made to reported adducts including the diazacyclooctane derivative, Ni-1·2SO2. Visual SO2 detection limits of Ni-1 and Ni-1?? are established at 25 ppm and 100 ppm, respectively. Structural studies of products resulting from reaction at the nucleophilic S-sites of (bme-dach)Ni and [(bme-dach)Zn]2 included acetyl chloride and sodium iodoacetate as electrophiles are shown. The acetyl group is a natural electrophile important to the citric acid cycle. Acetylation of (bme-dach)Ni produces a five coordinate, paramagnetic species. Iodoacetate is a cysteine modification agent known to inhibit enzymatic activity. The reaction of (bme-dach)Ni and sodium iodoacetate yields a blue, six coordinate nickel complex in a N2S2O2 donor environment. The bismercaptodiazacycloheptane ligand binds lead(II) forming an unprecedented structural form of N2S2M dimers, in which Pb2+ is largely bound to sulfur in a highly distorted trigonal geometry. Its unusual structure is described in comparison to other derivatives of the bme-daco ligand. The synthesis and structural characterization of square pyramidal (bme-dach)GaCl are also given and compared to the analogous (bme-daco)GaCl.

Cholesterol and fatty acyl-coenzymeA thioesters are signalling molecules with role in regulation of genes involved in lipid and glucose transport and metabolism. The studies described herein focused on three proteins that bind lipids and have different cellular functions: steroidogenic acute regulatory protein (StAR), hepatocyte nuclear factor-4a (HNF-4a) and acyl-CoA binding protein (ACBP). First, StAR mediates delivery of cholesterol to inner mitochondrial membrane in steroidogenesis by a poorly understood mechanism. In our studies, fluorescent NBD-cholesterol binding assays demonstrate that StAR binds cholesterol at two binding sites with 32 nM Kds and circular dichroism spectra show that cholesterol binding results in changes of StAR secondary structure. Fluorescent sterol exchange assays between donor and acceptor mitochondrial membranes indicate that StAR significantly increased the formation of rapidly transferable cholesterol domains. Second, HNF-4a, a nuclear receptor, had been shown to bind fatty acyl-CoAs as natural ligands with apparent low affinities obtained with radiolabeled ligand binding assays. Our fluorescence spectroscopy studies demonstrate that HNF-4a ligand binding domain (HNF-4aLBD) binds acyl-CoAs at a single binding site with Kds of 1.6-4 nM. Fluorescence resonance energy transfer (FRET) between HNF-4aLBD tryptophan residues and cis-parinaroyl-CoA yielded an intermolecular distance of 42 Â thus pointing to direct molecular interaction. Third, although ACBP has been detected in the nucleus, it is not known whether ACBP may directly and/or functionally interact with a nuclear acyl-CoA binding protein such as HNF-4a to regulate transcription. Our present studies in vitro and in intact cultured cells, including circular dichroism of HNF-4a in the presence of ACBP, coimmunoprecipitation of HNF-4a/ACBP complexes, ACBP and HNF-4a colocalization in nuclei of cells by confocal microscopy demonstrate a physical association of ACBP and HNF-4a. FRET microscopy data indicated an intermolecular distance of 53 Â between ACBP and HNF-4a in rat hepatoma cells. Functional assays (transactivation of an HNF4a-dependent reporter gene) showed significant increase in the presence of ACBP in two different cell lines. Expression of ACBP anti-sense RNA decreased HNF-4a-mediated transactivation, pointing to a role of ACBP in co-regulating HNF-4a-dependent transcription.

Electronic and steric parameters for square planar NiN2S2 complexes as bidentate, S-donor ligands have been established. According to the (CO) stretching frequencies and associated computed Cotton-Kraihanzel force constants of (NiN2S2)W(CO)4 adducts, a ranking of donor abilities and a comparison with classical bidentate ligands are as follows: Ni(ema)= > { [NiN2S2]0 } > bipy phen > Ph2PCH2CH2PPh2 > Ph2PCH2PPh2. In addition, we have demonstrated that the NiN2S2 ligands are hemilabile as evidenced from CO addition to (NiN2S2)W(CO)4, which is in equilibrium with the resulting (NiN2S2)W(CO)5 species (Keq = 2.8 M-1, G = -1.4 kJ/mole at 50C). Complete NiN2S2 ligand displacement by CO-cleavage of the remaining W-S bond to form W(CO)6 was not observed, indicating that the remaining W-S bond is considerably strengthened upon ring-opening. Several new cluster compounds based on the NiN2S2 ligands bound to CuI, RhI, PdII and W0 are reported. Structural analysis of (NiN2S2)MLn complexes show a unique structural feature defined by the dihedral angle formed by the intersection of NiN2S2/WS2C2 planes; placing the NiN2S2 ligand in closer proximity to one side of the reactive metal center. This unique orientational feature of the NiN2S2 ligands in the series of bimetallic compounds contrasts with classical diphosphine or diimine ligands. The "hinge angle" ranges in value from 136 as in the (Ni-1*)W(CO)4 to 101 in the (Ni-1)Pd(CH3)(Cl) complexes. The rigidity of the SR hinge of the nickeldithiolate ligands suggests that they might be suitable for stereochemical and regioselective substrate addition to catalytically active metals such as RhI and PdII.. The structural as well as functional similarities of the acetyl CoA synthase enzyme (ACS) and a palladium-metal based industrial type catalyst led to the preparation of a [(Ni-1)Pd(CH3)]+ bimetallic complex. This complex facilitates CO and ethylene copolymerization to produce polyketone similar to conventional (diphosphine)Pd(X)2 catalysts. However, the diphosphine ligands produce more efficient catalysts as the electron-rich character of the NiN2S2 ligand favors the resting state of the catalyst, [(Ni-1)Pd(C(O)CH3)(CO)]+, over the reactive form (Ni-1)Pd(C(O)CH3)(2-C2H4)]+. An exploratory investigation with the Ni-Pd heterobimetallic showed that this complex also facilitated the C-S coupling reaction to form a thioester similar to the ACS enzyme.

From opportunistic protist Cryptosporidium parvum we identified and functionally assayed a fatty acyl-CoA-binding protein (ACBP) gene. The CpACBP1 gene encodes a protein of 268 aa that is three times larger than typical ~10 KD ACBPs of humans and animals. Sequence analysis indicated that the CpACBP1 protein consists of an N-terminal ACBP domain (approximately 90 aa) and a C-terminal ankyrin repeat sequence (approximately 170 aa). The entire CpACBP1 open reading fragment (ORF) was engineered into a maltose-binding protein fusion system and expressed as a recombinant protein for functional analysis. Acyl-CoA-binding assays clearly revealed that the preferred binding substrate for CpACBP1 is palmitoyl-CoA. RT-PCR, Western blotting and immunolabelling analyses clearly showed that the CpACBP1 gene is mainly expressed during the intracellular developmental stages and that the level increases during parasite development. Immunofluorescence microscopy showed that CpACBP1 is associated with the parasitophorous vacuole membrane (PVM), which implies that this protein may be involved in lipid remodelling in the PVM, or in the transport of fatty acids across the membrane. We also identified two distinct oxysterol binding protein (OSBP)-related proteins (ORPs) from this parasite (CpORP1 and CpORP2). The short-type CpOPR1 contains only a ligand binding (LB) domain, while the long-type CpORP2 contains Pleckstrin homology (PH) and LB domains. Lipid-protein overlay assays using recombinant proteins revealed that CpORP1 and CpORP2 could specifically bind to phosphatidic acid (PA), various phosphatidylinositol phosphates (PIPs), and sulfatide, but not to other types of lipids with simple heads. Cholesterol was not a ligand for these two proteins. CpOPR1 was found mainly on the parasitophorous vacuole membrane (PVM), suggesting that CpORP1 is probably involved in the lipid transport across this unique membrane barrier between parasites and host intestinal lumen. Although Cryptosporidium has two ORPs, other apicomplexans, including Plasmodium, Toxoplasma, and Eimeria, possess only a single long-type ORP, suggesting that this family of proteins may play different roles among apicomplexans.

Triacylglycerols are the predominant molecules of energy storage in eukaryotes. Triacylglycerol synthesis is catalyzed by acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes, DGAT1 and DGAT2. Although the use of molecular tools, including targeted disruption of either DGAT enzyme, has shed light on their metabolic functions, little is known about the mechanisms responsible for regulating DGAT activity. Several lines of evidence from previous studies have suggested that DGAT1, but not DGAT2, is subject to regulation by phosphorylation and that protein kinase A (PKA)-dependent pathways are likely involved. In this study, the role of PKA in regulating DGAT activity and triacylglycerol synthesis during lipolysis was investigated. By using 3T3-L1 adipocytes, in vitro DGAT activity was shown to increase 2 fold during lipolysis. This data suggests that PKA might phosphorylate and activate DGAT1 during lipolysis to promote the recycling/re-esterification of excessive free fatty acids into triacylglycerols before they reach toxic levels within the cell. Additionally, high-performance liquid chromatography electrospray ionization mass spectrometry/mass spectrometry was exploited to identify PKA phosphorylation sites of DGAT1, and serine-17, -20 and -25 were identified as potential PKA phosphorylation sites using this methodology. The functional importance of these three potential phosphorylation sites was examined. Mutations of these sites to alanines (to prevent phosphorylation) or aspartates (to mimic phosphorylation) gave rise to enzymes functioning similarly to wild-type DGAT1. These phosphorylation sites appeared to be functionally silent as they were not involved in regulating DGAT1 activity, multimer formation, or enzyme stability. However, PKA phosphorylation at these three sites seemed to play a role in affinity of DGAT1 for its diacylglycerol substrate. These results indicate the existence of other unidentified, functionally active PKA phosphorylation sites or phosphorylation sites of other kinases, which are involved in regulating DGAT1.

L'enzim HMG-CoA reductasa (HMGR) catalitza la primera etapa limitant en la síntesi d'isoprenoides citosòlics. En plantes, és un enzim de membrana i la seva primera destinació subcel·lular és el reticle endoplasmàtic. Estructuralment, està formada per un domini amino-terminal (que inclou una regió amino-terminal citosòlica i dos fragments transmembrana) i un domini catalític altament conservat en tota l'escala evolutiva. En totes les espècies de plantes conegudes fins al moment, existeixen isoformes de l'HMGR codificades per diferents gens. Concretament, en Arabidopsis thaliana el gen hmg1 (expressat de forma majoritària) codifica per a les isoformes HMGR1S i HMGR1L, i el gen hmg2 (expressat a arrels, plàntules i inflorescències) codifica per a la isoforma HMGR2. A nivell d'estructura primària l'HMGR1L difereix de l'HMGR1S per la presència d'una regió extra de 50 residus aminoacídics a l'extrem amino-terminal. El domini amino-terminal confereix diferents destinacions de localització subcel·lular a la proteïna. En un treball anterior, es van identificar tres proteïnes que interaccionen amb les isoformes derivades del gen hmg1: AtB"&#945;, AtB"&#946; i AtKLC-1. Les dues primeres interaccionen específicament amb la regió amino-terminal de les isoformes HMGR1S i HMGR1L. Les proteïnes AtB"&#945; i AtB"&#946; són isoformes de la subunitat B" reguladora del complex proteïna fosfatasa 2A (PP2A). En el genoma d'A. thaliana hi ha cinc seqüències que codifiquen per a isoformes de la subunitat B" que comparteixen una gran homologia. En l'estructura primària de la subunitat B" s'han identificat motius EF-Hand (implicats en la unió a calci). S'ha demostrat que tant AtB"&#945; com AtB"&#946; uneixen calci. La tercera proteïna identificada, AtKLC-1, interacciona específicament amb la regió amino-terminal de l'HMGR1L. S'ha determinat per assaigs de doble híbrid en llevat i, posteriorment confirmats in vitro, que la PR65, proteïna estructural del complex PP2A, interacciona específicament amb l'AtKLC-1. La regió de la PR65 suficient per a la interacció amb la subunitat B" reguladora, AtB"&#945;, i amb l'AtKLC-1 comprèn la mateixa seqüència aminoacídica. Per tant, l'AtB"&#945; i l'AtKLC-1 podrien competir per a l'associació amb la PR65. Així, en la cèl·lula, la PP2A podria regular d'una forma particular les isoformes HMGR1S i HMGR1L. Assaigs in vivo i in vitro demostren que la PP2A és un regulador negatiu de l'enzim HMGR. Els ions calci inhibeixen també l'activitat HMGR. Per a què es dugui a terme la repressió de l'activitat HMGR tant per calci com per PP2A, es requereix el domini amino-terminal de la proteïna. Per tant, els resultats són consistents amb què les subunitats AtB" i/o AtKLC-1 duen a terme un paper mediador en la modulació de l'HMGR per la PP2A. El domini amino-terminal de l'HMGR1S està implicat en la morfogènesi de vesícules derivades del reticle endoplasmàtic. La subunitat AtB"&#945; i la resta del complex PP2A participen en aquest procés. El domini amino-terminal de l'HMGR1L dirigeix la proteïna a la trama de reticle endoplasmàtic. La PP2A participa també en la localització subcel·lular d'aquesta isoforma.S'ha caracteritzat una línia mutant en el gen hmg1 d'A. thaliana que mostra absència del transcrit hmg1 i una reduïda activitat HMGR. Les plantes d'aquest mutant creixen normalment en un medi de cultiu estèril i manifesten severes alteracions del desenvolupament quan són cultivades en terra. L'addició de mevalonat, producte de la reacció catalitzada per l'HMGR, no reverteix el fenotip. Les dades indiquen que el gen hmg1 duu a terme una funció no metabòlica relacionada amb l'adaptació al medi. En aquestes condicions de creixement, les estructures vesiculars induïdes per l'HMGR1S podrien tenir alguna funció essencial relacionada amb la resposta a estrès. / "ROLE OF THE PROTEINS AtKLC-1 AND AtB" IN THE REGULATION OF HMG-CoA REDUCTASE IN ARABIDOPSIS THALIANA".TEXT: The enzyme HMG-CoA reductase (HMGR) catalyses the formation of mevalonate in the first rate-limiting step of the mevalonate pathway for isoprenoid biosynthesis. All known plant HMGR isoforms are primarily targeted to the endoplasmic reticulum (ER).These proteins contain two domains: an N-terminal domain (which includes an N-terminal cytosolic region and two membrane-spanning sequences) and a conserved catalytic domain. In all plant species, there are a variety of HMGR isoforms encoded by a multigene family. In Arabidopsis thaliana, two genes (hmg1 and hmg2) encode three HMGR isoforms (HMGR1S, HMGR1L and HMGR2). Isoforms HMGR1S and HMGR1L are identical in sequence but HMGR1L is extended 50 amino acid residues at the N-terminal end. In a previous study, three proteins had been identified which specifically interact with the HMGR1L N-terminal end. Two of these proteins, designed AtB"&#61537; and AtB"&#61538;, are regulatory B" subunits of protein phosphatase 2A (PP2A). They bind the N-terminal region of HMGR1S and HMGR1L. The third one, AtKLC-1, exclusively interact with the N-terminal region of HMGR1L. In vitro assays have revealed that PR65, PP2A scaffolding subunit, specifically interact with AtKLC-1. Genetic and pharmacological approaches demonstrate that PP2A exerts an inhibitory control over HMGR. These results indicate that AtB" or AtKLC-1 could have a mediating role in the HMGR regulation carried out by PP2A. The N-terminal domain of the HMGR1S isoform is involved in the biogenesis of vesicle structures derived from the ER membranes. The PP2A complex is concerned in this process and the subunit AtB"&#61537; acts as an interceding factor. Furthermore, we have characterized an Arabidopsis thaliana insertion mutant for hmg1. This mutant exhibits no visible phenotype under sterile growth conditions but shows dwarfing and sterility when it is grown in a soil substrate. The addition of mevalonate doesn't rescue this phenotype. These data suggest that hmg1 performs a no-metabolic function related with environment adaptation. In this context, ER derived vesicles induced by HMGR1S could play an essential role related with stress response.

Triacylglycerols are the predominant molecules of energy storage in eukaryotes. Triacylglycerol synthesis is catalyzed by acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes, DGAT1 and DGAT2. Although the use of molecular tools, including targeted disruption of either DGAT enzyme, has shed light on their metabolic functions, little is known about the mechanisms responsible for regulating DGAT activity. Several lines of evidence from previous studies have suggested that DGAT1, but not DGAT2, is subject to regulation by phosphorylation and that protein kinase A (PKA)-dependent pathways are likely involved. In this study, the role of PKA in regulating DGAT activity and triacylglycerol synthesis during lipolysis was investigated. By using 3T3-L1 adipocytes, in vitro DGAT activity was shown to increase 2 fold during lipolysis. This data suggests that PKA might phosphorylate and activate DGAT1 during lipolysis to promote the recycling/re-esterification of excessive free fatty acids into triacylglycerols before they reach toxic levels within the cell. Additionally, high-performance liquid chromatography electrospray ionization mass spectrometry/mass spectrometry was exploited to identify PKA phosphorylation sites of DGAT1, and serine-17, -20 and -25 were identified as potential PKA phosphorylation sites using this methodology. The functional importance of these three potential phosphorylation sites was examined. Mutations of these sites to alanines (to prevent phosphorylation) or aspartates (to mimic phosphorylation) gave rise to enzymes functioning similarly to wild-type DGAT1. These phosphorylation sites appeared to be functionally silent as they were not involved in regulating DGAT1 activity, multimer formation, or enzyme stability. However, PKA phosphorylation at these three sites seemed to play a role in affinity of DGAT1 for its diacylglycerol substrate. These results indicate the existence of other unidentified, functionally active PKA phosphorylation sites or phosphorylation sites of other kinases, which are involved in regulating DGAT1.

From opportunistic protist Cryptosporidium parvum we identified and functionally assayed a fatty acyl-CoA-binding protein (ACBP) gene. The CpACBP1 gene encodes a protein of 268 aa that is three times larger than typical ~10 KD ACBPs of humans and animals. Sequence analysis indicated that the CpACBP1 protein consists of an N-terminal ACBP domain (approximately 90 aa) and a C-terminal ankyrin repeat sequence (approximately 170 aa). The entire CpACBP1 open reading fragment (ORF) was engineered into a maltose-binding protein fusion system and expressed as a recombinant protein for functional analysis. Acyl-CoA-binding assays clearly revealed that the preferred binding substrate for CpACBP1 is palmitoyl-CoA. RT-PCR, Western blotting and immunolabelling analyses clearly showed that the CpACBP1 gene is mainly expressed during the intracellular developmental stages and that the level increases during parasite development. Immunofluorescence microscopy showed that CpACBP1 is associated with the parasitophorous vacuole membrane (PVM), which implies that this protein may be involved in lipid remodelling in the PVM, or in the transport of fatty acids across the membrane. We also identified two distinct oxysterol binding protein (OSBP)-related proteins (ORPs) from this parasite (CpORP1 and CpORP2). The short-type CpOPR1 contains only a ligand binding (LB) domain, while the long-type CpORP2 contains Pleckstrin homology (PH) and LB domains. Lipid-protein overlay assays using recombinant proteins revealed that CpORP1 and CpORP2 could specifically bind to phosphatidic acid (PA), various phosphatidylinositol phosphates (PIPs), and sulfatide, but not to other types of lipids with simple heads. Cholesterol was not a ligand for these two proteins. CpOPR1 was found mainly on the parasitophorous vacuole membrane (PVM), suggesting that CpORP1 is probably involved in the lipid transport across this unique membrane barrier between parasites and host intestinal lumen. Although Cryptosporidium has two ORPs, other apicomplexans, including Plasmodium, Toxoplasma, and Eimeria, possess only a single long-type ORP, suggesting that this family of proteins may play different roles among apicomplexans.

[N,N??-bis-(mercaptoethyl)-1,5-diazacyclooctanato]NiII, Ni-1, is known to undergo metallation reactions with numerous metals. [N,N??-bis-(mercaptoethyl)-1,5-diazacycloheptanato]NiII, (bme-dach)Ni or Ni-1??, differs from Ni-1 by one less carbon in its diazacycle backbone ring producing subtle differences in N2S2Ni geometry. Metallation of Ni-1?? with PdCl2, Pd(NO3)2, and NiBr2 produced three structural forms: Ni2Pd basket, Ni4Pd2 C4-paddlewheel, and Ni3 slant chair. In attempts to provide a rationale for the heterogeneity in the active site of Acetyl coA Synthase, metal ion capture studies of Ni-1 in methanol found a qualitative ranking of metal ion preference: Zn2+ < Ni2+ < Cu+. Formation constants for metal ion capture of Ni-1?? in water were determined for Pb2+, Ni2+, Zn2+, Cu+, and Ag+. A quantitative estimate places copper some 15 orders of magnitude above nickel or zinc in binding affinity. Sulfur dioxide uptake by Ni-1?? is characterized by significant color change, improved adduct solubility, and reversible binding of two equivalents of SO2. These combined properties establish Ni-1?? as a suitable model for gas uptake at nickel thiolate sites and as a possibly useful chemical sensor for this poisonous gas. Comparisons of molecular structures,&#61472; &#957;(SO) stretching frequencies, and thermal gravimetric analyses are made to reported adducts including the diazacyclooctane derivative, Ni-1&#903;2SO2. Visual SO2 detection limits of Ni-1 and Ni-1?? are established at 25 ppm and 100 ppm, respectively. Structural studies of products resulting from reaction at the nucleophilic S-sites of (bme-dach)Ni and [(bme-dach)Zn]2 included acetyl chloride and sodium iodoacetate as electrophiles are shown. The acetyl group is a natural electrophile important to the citric acid cycle. Acetylation of (bme-dach)Ni produces a five coordinate, paramagnetic species. Iodoacetate is a cysteine modification agent known to inhibit enzymatic activity. The reaction of (bme-dach)Ni and sodium iodoacetate yields a blue, six coordinate nickel complex in a N2S2O2 donor environment. The bismercaptodiazacycloheptane ligand binds lead(II) forming an unprecedented structural form of N2S2M dimers, in which Pb2+ is largely bound to sulfur in a highly distorted trigonal geometry. Its unusual structure is described in comparison to other derivatives of the bme-daco ligand. The synthesis and structural characterization of square pyramidal (bme-dach)GaCl are also given and compared to the analogous (bme-daco)GaCl.