Purification and regulatory properties of pig kidney AMP deaminase

AMP deaminase (EC 3.5.4.6) from pig kidney was purified about 1200-fold by chromatography on cellulose phosphate. The enzyme showed a sigmoid-shaped substrate saturation curve which was converted to hyperbolic by addition of ATP. The ATP-activated enzyme was sensitive to phosphatidylcholine-containing liposomes which caused a further increase of activity by lowering the S0.5 value and increasing V max. In the absence of ATP, the enzyme was not sensitive to phosphatidylcholine-containing liposomes. Phosphatidate-containing liposomes exerted an inhibitory effect both in the presence and absence of ATP. In the presence of ATP phosphatidate was a non-competitive inhibitor. Orthophosphate was found to be a competitive inhibitor of AMP deaminase from pig kidney. When the phosphatidylcholine/phosphatidic acid ratio in liposomes was 2.7, AMP deaminase was activated, whereas when this ratio dropped below 2.1, liposomes exerted a non-competitive inhibitory effect.