Properties of acetate kinase activity inClostridium thermocellum cell extracts

Acetate kinase (EC 2.7.2.1) is involved in the wasteful production of acetate during conversion of cellulose to ethanol byClostridium thermocellum. The properties of this enzyme activity inC. thermocellum cell extracts were determined. Optimum enzyme activity was at 60°C and between pH 7.5 and 9.0. In the presence of air, acetate kinase was stable to temperatures up to 60°C, retaining 90% activity after 2 h, and was inactivated rapidly at higher temperatures. The enzyme exhibited a wide range of stability to pH (5.0-9.0) when incubated at 50°C for 2 h. As with other acetate kinases, a divalent cation, such as Mg^sup 2+^, was required for enzyme activity. Optimum activity was observed at 20mM MgCl^sub 2^ when ATP was held constant at 10 mM. Acetate kinase activity was adversely affected by KCl, a salt commonly used in ion-exchange or affinity chromatography, with 0.3M KCl inhibiting by 50%. These results will be important in optimizing the direct microbial conversion process of cellulose to ethanol usingC. thermocellum in coculture withClostridium thermosaccharolyticum.[PUBLICATION ABSTRACT]