ABSTRACT
The properties of piglet cardiac AMP deaminase were determined and its regulation by pH, phosphate, nucleotides and phosphorylation is described. AMP deaminase purified from the ventricles of newborn piglet hearts displayed hyperbolic kinetics with a Km of 2 mM for 5'-AMP. The enzyme had a pH optimum of 7.0 and was strongly inhibited by inorganic phosphate. ATP decreased the Km of the native enzyme 3-fold, but did not significantly block the inhibitory effects of phosphate. Kinetic parameters were not significantly altered in the presence of adenosine, cyclic AMP and NAD+, whereas, the Km was decreased by 50% in the presence of NADH. Piglet cardiac AMP deaminase was phosphorylated by protein kinase C, resulting in a 2-fold increase in Vmax with no change in Km. However, incubation with cAMP-dependent protein kinase did not affect enzyme kinetics. The 80-85 kD protein subunit of piglet cardiac AMP deaminase immunoreacted with antisera raised against human erythrocyte AMP deaminase, rabbit heart AMP deaminase and human recombinant AMP deaminase 3 (isoform E). These results are discussed in relation to in situ AMP deaminase activity in neonatal piglet heart myocytes.