AMP deaminase from spinach leaves purification and some regulatory properties

Simmary AMP deaminase (EC 3.5.4.6) was found to be present in particulate and cytosol fractions obtained from spinach leaf extracts. The cytosol AMP deaminase was partially purified by fractionation with ammonium sulfate and phosphocellulose chromatography. The enzyme is specific for AMP as substrate, and shows cooperative binding of AMP (Hill coefficient, n H = 1.6) with S 0.5 values of 10 mM. ATP and alkali metals act as positive effectors, lowering n H to 1.0 and S 0.5 to 0.25 and 2 mM, respectively. Pi inhibits the enzyme in an allosteric manner. Kinetic properties of AMP deaminase suggest that the enzyme is in the activated state under physiological conditions, and may be regulated by changes in AMP and Pi concentrations. The occurrence and regulatory properties of AMP deaminase in spinach leaves could account for changes in adenine nucleotide levels during photosynthesis in leaf cells.