Abstract
1. 1. The enzyme AMP aminohydrolase (EC 3.5.4.6) was purified about 90-fold from the 105 000 × g supernatant of rat liver. The procedure consisted of Li 2SO 4 precipitation, heat treatment, chromatography over DEAE-cellulose, and gel filtration over Sepharose 4B. 2. 2. The purified enzyme had a pH optimum between 6.0 and 6.2 3. 3. ATP and alkali metal ions strongly activated the enzyme. GTP activated the enzyme at low concentrations of substrate, but was inhibitory at high substrate concentrations. When GTP and ATP were added to the reaction mixture simultaneously, it was found that GTP was a potent inhibitor of ATP activation. 4. 4. Comparison of the properties of the enzyme isolated from rat liver are made with that isolated from other tissue, especially muscle and brain, and differences noted. 5. 5. The data are consistent with the hypothesis that this is an allosteric enzyme, and that its intracellular regulation may be accomplished by the ratio of AMP-ATP-GTP.
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