ADENOSINE 5'-TETRAPHOSPHATE AND ADENOSINE 5'-PENTAPHOSPHATE ARE SYNTHESIZED BY YEAST ACETYL-COENZYME-A SYNTHETASE

Yeast (Saccharomyces cerevisiae) acetyl coenzyme A (CoA) synthetase (E C 6.2.1.1) catalyzes the synthesis of adenosine 5'-tetraphosphate (p(4 )A) and adenosine 5'-pentaphosphate (p(5)A) from ATP and tri- or tetra polyphosphate (P-3 or P-4), with relative velocities of 7:1, respectiv ely. Of 12 nucleotides tested as potential donors of nucleotidyl moiet y, only ATP, adenosine-5'-O-[3-thiotriphosphate], and acetyl-AMP were substrates, with relative velocities of 100, 62, and 80, respectively. The K-m values for ATP, P-3, and acetyl-AMP were 0.16, 4.7, and 1.8 m M, respectively. The synthesis of p(4)A could proceed in the absence o f exogenous acetate but was stimulated twofold by acetate, with an app arent K-m value of 0.065 mM. CoA did not participate in the synthesis of p(4)A (p(5)A) and inhibited the reaction (50% inhibitory concentrat ion of 0.015 mM). At pH 6.3, which was optimum for formation of p(4)A (p(5)A), the rate of acetyl-CoA synthesis (1.83 mu mol mg(-1) min(-1)) was 245 times faster than the rate of synthesis of p(4)A measured in the presence of acetate. The known formation of p(4)A (p(5)A) in yeast sporulation and the role of acetate may therefore be related to acety l-CoA synthetase.