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

Yeast (Saccharomyces cerevisiae) acetyl coenzyme A (CoA) synthetase (EC 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 tetrapolyphosphate (P-3 or P-4), with relative velocities of 7:1, respectively. Of 12 nucleotides tested as potential donors of nucleotidyl moiety, 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 mM, respectively. The synthesis of p(4)A could proceed in the absence of exogenous acetate but was stimulated twofold by acetate, with an apparent 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 concentration 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 acetyl-CoA synthetase.