6- -purines, formation

Thus, 2-methylthio-4,6,7-triphenylpteridine is a mM reactive compound. It shows activity to nucleophiles at four ring carbon atoms at C-4 [Sn(AN-RORC)], at C-2 [Sn(AE)], and at C-6, as well as at C-7 (purine formation). Based on qualitative product studies and N-label incorporation studies, the order of reactivity is approximately C-4 > C-2 > C-7 > C-6. 

All cells must be able to make pyrimidine and purine bases to be used in synthesis of nucleic acids and coenzymes. The pathway for synthesis of pyrimidine begins with aspartic acid and that for purines with glycine. In many organisms the pathway of purine formation is further enhanced because uric acid or a... 

PRPP is the activated intermediate in the synthesis of phosphoribosylamine in the de novo pathway of purine formation of purine nucleotides from free bases by the salvage pathway of orotidylate in the formation of pyrimidines of nicotinate ribonucleotide of phosphoribosyl ATP in the pathway leading to histidine and of phosphoribosylanthranilate in the pathway leading to tryptophan. 

Increased levels of intracellular PRPP enhance de novo purine biosynthesis. For example, in patients with HPRT deficiency, the fibroblasts show accelerated rates of purine formation. Several mutations of PRPP synthetase, which exhibit increased catalytic activity with increased production of PRPP, have been described in gouty subjects. 

This type of purine formation is a so-called abiotic synthesis [150]. This is defined as the synthesis of compounds essential for living organisms from nonbiological material in the course of chemical evolution. 

However, if this were true, the carbon atoms of glycine, which is known to contribute to purine formation, should be found in histidine by isotopic methods. When this was put to test with glycine-l-C, no radioactivity was found in the histidine of growing yeast. ... 

Fig. 4. Pathways of purine formation and AIC utilization in pigeon liver.

Since aminoribosylimidazolecarboxamide phosphate is not a known precursor for purine biosynthesis and various experimental results were obtained which indicated that this compound was not being utilized for purine formation by the bacterial preparations, Moyed and Magasanik were led to suspect that this compound was involved in the biosynthesis of the imidazole ring of histidine. This suggestion was supported by the finding of the accumulation of D-erj/ffiro-imidazoleglycerol phosphate ester as a product of these reactions. 

Since AICA per se was not believed to be an intermediate in purine formation, the possibility of ribonucleotide participation in its metabolism was also investigated 66). When labeled AICA was incubated for short periods of time with banks of nonisotopic IMP and either hypoxanthine or... 

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