Isozymes of AMP Deaminase

Abstract

AMP deaminase (AMP aminohydrolase EC, 3.5.4.6) catalyzes deamination of AMP to form IMP and ammonia. Although the physiological role of this enzyme remains obscure, it may be important to stabilize the adenylate charge (1), in the conversion of adenine nucleotide to inosine or guanine nucleotide (2–5) and furthermore as a key enzyme in the purine nucleotide cycle (6–10). The deaminase exists in multiple molecular forms in different rat tissues (11–15). On the basis of chromatographic, immunological, and kinetic properties, three parental forms (types A, B and C) have been detected in rat tissues. They could be resolved by phosphocellulose column chromatography, and with respect to immunological properties, no crossreactivity occures between types A, B and C. All these three parental isozymes have a sigmoidal velocity profile with respect to AMP in the absence of activators, and are modified by alkali metals and nucleotides. Type A AMP deaminase is the only form found in skeletal muscle and is also the major isozyme in diaphragma. Type B AMP deaminase is the major isozyme of kidney, liver and testis. Type C AMP deaminase is the only form found in heart. Other tissues such as brain, spleen, and lung, where the multiple molecular forms exist, showed the B and C type parental isozymes and presumably three B–C hybrids, while no A type isozyme was observed in these tissues.