The guanine nucleotides (rtbo and deoxyribo) serve many important roles in biosynthesis and btological control. They are involved in the synthesis of enzymes (1 ), and are allosteric regulators for such enzymes as glutamate dehydrogenase (2 ) and acetyl-CoA carboxylase (3 ). They regulate IMP dehydrogenase gene expression (4 ). The guanine nucleotldes are incorporated into DNA and RNA (5 ), are substrates in the Krebs tricarboxylic acid cycle (6 ), and function in microtubule assembly (7 ). Guanine nucleotides regulate the activation of adenylate cyclase vta G proteins in receptor-mediated signalmg processes (8 –11 ). The G-proteins are involved in ion channel function (12 ). Guanylates also serve as coenzymes functioning in such physiological responses as vision (13 ), bactertal sporulation (14 ), and the stringent response to amino acid deprivation (15 ).
