Effect of Salts on Inhibition of Chicken Muscle Adenosine Monophosphate Deaminase by Phosphate Esters and Inorganic Phosphate EFFECT OF 5,5’-DITHIOBIS(2-NITROBENZOIC ACID) ON ENZYME ACTIVITY AND INHIBITION

Inhibition of purified AMP-deaminase from chicken breast muscle by phosphate esters and inorganic phosphate has been investigated. When tested at a concentration of 3 mM, in the presence of 0.15 M potassium chloride, the order of effectiveness as inhibitors of deaminase activity was: 2,3diphosphoglyceric acid, 3-phosphoglyceric acid, 2-phosphoglyceric acid, 2-phosphoenolpyruvate, fructose 1,6diphosphate, ribose S-phosphate, P-glycerophosphate r,-ar-glycerophosphate, glucose 6-phosphate, glucose l-phosphate, and fructose l-phosphate. Inhibition by 2,3-diphosphoglyceric acid, d-phosphoglyceric acid, 2-phosphoenolpyruvate, and r,-a-glycerophosphate was also tested in the absence of potassium chloride; the degree of inhibition was depressed. In contrast to inhibition by phosphate esters, addition of potassium chloride sharply reduced the degree of inhibition by inorganic phosphate. The effects of salts on enzyme activity and inhibition by 2,3-diphosphoglyceric acid have been compared. When tested at 0.15 M salt and in the presence of 95 PM 5’-AMP, the order of effectiveness as activators of enzyme activity was potassium chloride, lithium chloride, ammonium chloride, sodium chloride, rubidium chloride, cesium chloride, and tetramethylammonium chloride. Ammonium, rubidium, potassium, and sodium chlorides enhanced the level of inhibition by 2,3-diphosphoglyceric acid approximately 2-fold. The effect was somewhat less with tetramethylammonium chloride and was negligible with lithium chloride. The role of sulfhydryl groups in inhibition by 2,3-diphosphoglyceric acid, with and without sodium chloride, and their effect on catalytic activity have also been investigated. Native deaminase, as well as enzyme which had been denatured in 0.3 % sodium dodecyl sulfate, was titrated with 5,5’-