Extracts of acetate-grown Methanosarcina thermoghila were assayed
for the presence of enzymes which might catalyze a proposed activation
of acetate as the initial step in the pathway of methanogenesis from
acetate by that organism. Acetate kinase and phosphate
acetyltransferase activities of 4.9 and 49 μmoles of product/min/mg
protein, respectively, were detected. Acetate kinase was purified 102-
fold to a specific activity of 656 μmoles ADP formed/min/mg protein and
was essentially homogeneous by denaturing gel electrophoresis. The
native enzyme (Mr 94,000) was an α2 homodimer with a subunit Mr of
53,000. Activity was optimal between pH 7.0 and 7.4 and was stable to
heating at 70°C for 15 min. The apparent Km for acetate was 22 mM
(Vmax = 668 μmoles ADP/min/mg protein) and 2.8 mM for ATP (Vmax = 777
pmoles ADP/min/ protein). The enzyme phosphorylated propionate at 602
of the rate with acetate but was unable to use formate. TTP, ITP, UTP,
GTP, and CTP replaced ATP as the phosphoryl donor to acetate. One of
several divalent cations was required for activity; the maximum rate
was obtained with Mn2+.
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