1. The activities of the purine phosphoribosyltransferases (EC 2.4.2.7 and 2.4.2.8) in purine-analogue-resistant mutants of Schizosaccharomyces pombe were checked. An 8-azathioxanthine-resistant mutant lacked hypoxanthine phosphoribosyltransferase, xanthine phosphoribosyltransferase and guanine phosphoribosyltransferase activities (EC 2.4.2.8) and appeared to carry a single mutation. Two 2,6-di...

It has been reported that the capacity of rabbit bone marrow to carry out the synthesis de novo of purine ribonucleotides is quite low, and that this tissue requires preformed purine derivatives supplied by the liver (1, 2). Presumably, the salvage enzymes, including nucleoside phosphorylases (3),. participate in the reutilization of the preformed derivatives. So far, only pyrimidine nucleoside...

Mouse lymphoma L5178Y cells in culture were syn chronized by exposure to thymidine and Colcemid. At four times during the cell cycle, various aspects of purine metab olism were examined with the use of radioactive purine bases. In all experiments the uptake and conversion of bases to nucleotides was rate limiting for ribonucleoside triphosphate synthesis. Cell cycle variations in the apparent e...

Microorganisms that require p-aminobenzoic acid or compounds of the folic acid group may have either requirement replaced by a purine and thymine (or thymidine) and several amino acids or vitamin B12 (Lampen et al., 1949; Stokstad, 1941; Baker et al., 1955); the vitamins, p-aminobenzoic or folic acids, are believed necessary for the synthesis of those compounds which can bypass them (Shive, 195...

The contribution of reduced purine salvage to the hyperuricemia associated with hypoxanthine-guanine phosphoribosyltransferase deficiency was measured by the intravenous administration of tracer doses of [8-(14)C]adenine to nine patients with normal enzyme activity, three patients with a partial deficiency of hypoxanthine-guanine phosphoribosyltransferase, and six patients with the Lesch-Nyhan ...

There is evidence that an interchange of purines among tissues may occur (1, 2) and that, for example, bone marrow obtains its purines from the liver (3). For this reason relative rates of purine synthesis de novo in organs, as indicated by incorporation of a radioactive precursor, may be ambiguous if measured at relatively long times after administration of the precursor. Therefore the synthes...

Purine metabolism in Giardia lamblia was investigated by monitoring incorporation of radiolabeled precursors into purine nucleotides in the log-phase trophozoites cultivated in vitro in axenic media and incubated in buffered saline glucose. The lack of incorporation of formate, glycine, hypoxanthine, inosine, and xanthine into the nucleotide pool suggests the absence of de novo purine nucleotid...

Previous experiments have shown that when hypoxanthine is synthesized de novo from formate, glycine, and CO2 in extracts or homogenates of pigeon liver these substrates are utilized for purine synthesis in the molecular ratio of 2: 1: 1 (1). Formate is the precursor of carbon atoms 2 and 8 of the purine base; glycine, of atoms 4, 5, and 7; and CO2 of atom 6 (2, 3). The present problem originate...

The objectives of the present study were to estimate the microbial-N flow to the small intestine and to predict the digestible organic matter intake (DOMI) in grazing Karayaka sheep based on urinary excretion of purine derivatives (xanthine, hypoxanthine, uric acid, and allantoin) by the use of spot urine sampling under field conditions. In the trial, 10 Karayaka sheep from 2 to 3 years of age ...

About 20 % of ruminal microbial N in dairy cows derives from purines and pyrimidines; however, their intermediary metabolism and contribution to the overall N metabolism has sparsely been described. In the present study, the postprandial patterns of net portal-drained viscera (PDV) and hepatic metabolism were assessed to evaluate purine and pyrimidine N in dairy cows. Blood was sampled simultan...