ATP-dependent glucokinase from the hyperthermophilic bacteriumThermotoga maritimarepresents an extremely thermophilic ROK glucokinase with high substrate specificity

The gene (open reading frame (ORF) Tm1469, glk) encoding ATP-dependent ROK (repressors, ORFs, sugar kinases) glucokinase (ATP-GLK, EC 2.7.1.2) of the hyperthermophilic bacterium Thermotoga maritima was cloned and functionally expressed in Escherichia coli. The purified recombinant enzyme is a homodimer with an apparent molecular mass of 80 kDa composed of 36-kDa subunits. Rate dependence (at 80°C) on glucose and ATP followed Michaelis–Menten kinetics with apparent Km values of 1.0 and 0.36 mM, respectively; apparent Vmax values were about 370 U mg−1. The enzyme was highly specific for glucose as phosphoryl acceptor. Besides glucose only 2-deoxyglucose was phosphorylated to some extent, whereas mannose and fructose were not used. With a temperature optimum of 93°C the enzyme is the most thermoactive bacterial ATP-GLK described.