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Kinetic Properties of Phosphotransacetylase from Veillonella alcalescens

¹ Department of Microbiology, University of Washington, Seattle, Washington 98195

ABSTRACT

The phosphotransacetylase of Veillonella alcalescens catalyzes a reversible reaction with Michaelis-Menten kinetics for all substrates. The rate of the reverse reaction (the synthesis of acetyl coenzyme A from acetyl phosphate) was 6.5 times greater than the rate of the forward reaction (the synthesis of acetyl phosphate from acetyl coenzyme A). The apparent K_m values determined for the forward reaction were 8.6 x 10^–6M for acetyl coenzyme A and 9.3 x 10^–3M for phosphate. In the reverse reaction, the K_m values were 3.3 x 10^–4M for coenzyme A and 5.9 x 10^–4M for acetyl phosphate. The results of an analysis of the inhibition by end products in the forward and reverse directions were compatible with a random bi- bi- mechanism. The enzyme was inhibited by adenosine triphosphate and adenosine diphosphate but was not affected by reduced nicotinamide adenine dinucleotide or pyruvate. The inhibition by adenosine triphosphate was noncompetitive with respect to acetyl phosphate and competitive with respect to coenzyme A. MgCl₂ reversed the inhibition by adenosine triphosphate or adenosine diphosphate. The role of Mg²⁺ and adenylates in the regulation of phosphotranscetylase activity is discussed.

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