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Thesis (M.A.)--Boston University / In studies on the formation of 2,3-diphosphoglycerate (2,3-DPG) from inosine by erythrocyte preparations it was observed that the inosine interfered with the enzymatic assay for 2,3-DPG. Phosphoglyceromutase, for which 2,3-DPG is a coenzyme, and enolase were used in a coupled assay. The inosine appeared to interfere by inhibiting the enolase [TRUNCATED]

Graduation date: 1995

The nucleic acids digested by ruminants are essentially of microbial origin. Absorbed purines are extensively degraded and excreted in urine as allantoin, uric acid, xanthine and hypoxanthine. The measurement of the urinary purine derivatives could be used to estimate the uptake of purines and hence that of microbial protein. 1) Automated methods for measurements of purine derivatives were improved. A HPLC method for determining total adenine and guanine was used to measure the purine contents of mixed rumen bacteria and the digestibility of microbial purines in sheep. 2) Endogenous excretions of purine derivatives by sheep and cattle of different physiological states were measured using animals nourished by intragastric infusions of VFA and casein. The species difference in and the effects of changes in protein supply on the endogenous excretion were studied. 3) A microbial nucleic acid extract was infused into the abomasum of lambs at 6 levels. The subsequent urinary excretion of purine derivatives was examined. The results suggested that exogenous purines were utilised by the sheep. A model is proposed to describe the relationship between purine derivative excretion and purine uptake. 4) Allantoin was infused intravenously to sheep and the changes in plasma concentration, nephric tubular re-absorption and urinary excretion of allantoin were studied. Results showed that plasma allantoin was rapidly removed and a constant proportion of the allantoin entering the blood was excreted in urine of sheep. 5) Secretion of allantoin and uric acid into the gut via saliva was quantified in sheep. The possible decomposition of the allantoin in the rumen by microbes in the rumen fluid and in the rumen wall of sheep was examined <i>in vitro</i> and <i>in vivo</i>. Allantoin infused into the rumen or abomasum of sheep and cattle was not recovered in urine. 6) A model for calculation of microbial protein available to sheep is proposed. It is suggested that a different model should be used for cattle. These models were applied in two feeding experiments with sheep and steers.

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2004. / Includes bibliographical references.

PNP is a crucial enzyme in purine metabolism, and its inherited defects result in severe T-lineage immune deficiency in humans. I hypothesized that PNP deficiency disrupts the development of late CD4-CD8- double negative (DN) thymocytes and induces mitochondrial-mediated apoptosis of CD4+CD8+ double positive (DP) thymocytes. By using PNP-deficient (PNP-/-) mice as well as an OP9-DL1 co-culture system simulating PNP-deficient conditions, I demonstrated that PNP deficiency interferes with the maturation of DN thymocytes at the transition from DN3 to DN4 stage. Although PNP deficiency does not affect the generation or proliferation of DP thymocytes, PNP-/- DP thymocytes were observed to undergo apoptosis at a higher rate. My results suggest that apoptosis is induced through a mitochondrial mediated pathway. Additionally, re-introduction of PNP into PNP-/- thymocytes protected the cells from the toxic effects of deoxyguanosine by preventing the formation of deoxyguanosine triphosphate, indicating that the toxic metabolite in PNP deficiency is deoxyguanosine.