Phosphotransferases acetate kinase

Buss KA, Cooper DR, Ingram-Smith C, et al. 2001. Urkinase structure of acetate kinase, a member of the ASKHA superfamily of phosphotransferases. J Bacte-riol 183 680-6. 

This phosphotransferase [EC 2.7.2.1] catalyzes the thermodynamically favored phosphorylation of ADP to form ATP Aeq = [ATP][acetate]/ [acetyl phosphate] [ADP] = 3000). GDP is also an effective phosphoryl group acceptor. This enzyme is easily cold-denatured, and one must use glycerol to maintain full catalytic activity. Initial kinetic evidence, as well as borohydride reduction experiments, suggested the formation of an enzyme-bound acyl-phosphate intermediate, but later kinetic and stereochemicaT data indicate that the kinetic mechanism is sequential and that there is direct in-line phosphoryl transfer. Incidental generation of a metaphosphate anion during catalysis may explain the formation of an enzyme-bound acyl-phosphate. Acetate kinase is ideally suited for the regeneration of ATP or GTP from ADP or GDP, respectively. 

Occasionally, one can maintain initial rate conditions by using a coupled reaction system to regenerate one of the limiting substrates. For example, to regenerate ATP in a phosphotransferase reaction, one can use creatine phosphate and creatine kinase acetylphosphate and acetate kinase or phosphoenolpyruvate and pyruvate kinase. 

M. soehngenii lacks acetate kinase, phosphotransacetylase, and PPi AMP- or PPi ADP-phosphotransferase[241], but possesses high levels of adenylate kinase (Reaction 37) and pyrophosphatase (Reaction 38) activities ... 

Desulfotomaculum is able to conserve the energy of the PPj produced by ATP-sulfurylase (reaction 3) by means of the enzyme acetate PPj phosphotransferase (reaction 4). ATP can then be produced from acetylphosphate and ADP by acetate kinase (reaction 5). 

The biosynthetic pathway that produces bacterial cellulose from glucose and fructose is shown in Fig. 14.2. Glucose is phosphorylated by glucose hexokinase and not by the phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS). The resulting glucose-6-phosphate (G6P) is metabolized through the pentose pathway, because the activity of fructose-6-phosphate (F6P) kinase, which phos-phorylates F6P to fructose-1,6-diphosphate (FDP), is absent in acetic acid bacteria. 

Fig. 14.2 Cellulose biosynthetic pathway in cellulose-producing acetic acid bacteria. FIP firuc-tose-1-phosphate, F6P fructose-6-phosphate, FDP fructose diphosphate, PGA phosphogluconate GHK glucose hexokinase, FHK fructose hexokinase, IPFK fructose-1-phosphate kinase, FBP fructose blsphosphatase, PGI phosphoglucose isomerase, PGM phosphoglucomutase, UGP UDP-glucose pyrophosphorylase, G6PD glucose-6-phosphate dehydrogenase, PTS phosphotransferase system EMP Embden-Myerhoff pathway...

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