Substrate Specificity and Aspects of Deamination Catalyzed by Rabbit Muscle 5'-Adenylic Acid Aminohydrolase

A total of 24 nucleotides were examined as substrates for 5'-AMP aminohydrolase (EC 3.5.4.6). The following nucleotides were deaminated at the indicated maximum velocity relative to AMP (100): adenosine 5'-phosphoramidate (73), N6-methyl-AMP (20), dAMP (18), adenosine 5'-monosulfate (13), adenosine (1), and ADP (1). Other substrates for which maximum velocities were not determined included N6-ethyl6-AMP, formycin 5'-monophosphate, 2'-O-methyl-ADP, and α,β-methylene-ADP. 3'-AMP, 3',5'-AMP, and 3-β-d-ribofuranosyladenine 5'-phosphate were not deaminated but were effective inhibitors. The pH optimum for ADP deamination was more acidic (pH 5.0 to 5.5) than the optima for AMP or adenosine (pH 6.3 to 7.0). Heat inactivation data and the concurrent elution of the activity for AMP and ADP from cellulose phosphate are consistent with a single enzyme being responsible for the multiple activities. Aspects of the mechanism are discussed.