Abstract
This chapter discusses the carbon and nitrogen transfer reactions in nucleotide metabolism. The chapter also presentsthe glutamine amide transfer reactions of purine and pyrimidine biosynthesis de novo, and of purine and pyrimidine ribonucleotide interconversion, and several more that occur in other areas of metabolism. In most cases, NH3 is able to replace glutamine as the nitrogen donor. However, it is NH3 rather than NH4+ that participates in these reactions, so that at pH 7.4 the total (NH3 + NH4+) concentration must be about 100 times that of glutamine to give the same reaction rate. Therefore, it would appear that in these reactions glutamine brings to the enzyme an uncharged nitrogen atom at the oxidation level of ammonia. The physiological importance of the replacement of glutamine by NH3 appears to vary from enzyme to enzyme, and even from organism to organism for the same enzyme. In most cases, hydroxylamine can replace ammonia as substrate, the corresponding hydroxylamino derivative being a product.
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