Abstract
AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) was found in extract of baker's yeast ( Saccharomyces cerevisiae), and was purified to electrophoretic homogeneity using phosphocellulose adsorption chromatography and affinity elution by ATP. The enzyme shows cooperative binding of AMP (Hill coefficient, n H , 1.7) with an s 0.5 value of 2.6 mM in the absence or presence of alkali metals. ATP acts as a positive effector, lowering n H to 1.0 and s 0.5 to 0.02 mM. P i inhibits the enzyme in an allosteric manner: s 0.5 and n H values increase with increase in P i concentration. In the physiological range of adenylate energy charge in yeast cells (0.5 to 0.9), the AMP deaminase activity increases sharply with decreasing energy charge, and the decrease in the size of adenylate pool causes a marked decrease in the rate of the deaminase reaction. AMP deaminase may act as a part of the system that protects against wide excursions of energy charge and adenylate pool size in yeast cells. These suggestions, based on the properties of the enzyme observed in vitro, are consistent with the results of experiments on baker's yeast in vivo reported by other workers.
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