Adenylic Acid Deaminase of Rat Liver.

The existence of a specific deaminase in muscle tissue for the deamination of adenylic acid (AMP) was firmly established by its crystallization and characterization (l-3). Whether hepatic tissue also had a specific AMP deaminase appeared less certain. For instance, Conway and Cooke (4) believed that the deamination of AMP in rabbit liver was preceded by dephosphorylation. On the other hand, Kutscher and Sarreither (5), who studied AMP deamination in carbonate extracts of cat and chicken liver, attributed ammonia evolution to an AMP deaminase. Chan, McCoy, and Kizer (6) concluded that AMP was deaminated at the nucleotide level by rat liver homogenates ince, in their studies, ammonia evolution was not accompanied by proportional increases in inorganic phosphate levels. Purzycka and Zydowo (7) subjected rat liver homogenates to a fractionation procedure which yielded a fraction that converted AMP to inosinic acid (IMP) and ammonia, but this fraction had no detectable adenosine deaminase activity. Recently the problem was reinvestigated by Fiala and Kasinsky (8), and they concluded that the enzymatic deamination of AMP by rat liver was catalyzed by two enzymes, a phosphatase and adenosine deaminase. It was their contention that rat liver possessed no enzyme for the direct deamination of AMP to IMP. Since these findings conflicted with our earlier work (6) and the work of Purzycka and Zydowo (7), we set out to determine whether rat liver contained an enzyme for the direct deamination of AMP to IMP and whether previous conflicting conclusions could be rationalized. This paper describes experiments that led us to conclude that rat liver and rat tumors of hepatic origin contained an active, specific AMP deaminase.