PHOSPHORYLATION OF GLUCOSE BY A GUANOSINE-5'-TRIPHOSPHATE (GTP)-DEPENDENT GLUCOKINASE IN FIBROBACTER-SUCCINOGENES SUBSP SUCCINOGENES S85

Cell extracts of Fibrobacter succinogenes subsp. succinogenes S85 phos phorylated glucose with a GTP-dependent glucokinase. The enzyme showed little activity with ATP (12% of that with GTP). Of other phosphate d onors tested, only dGTP and ITP gave high glucokinase activities. Dial yzed extracts required Mg+2 and K+ for maximal activity. In potassium phosphate buffer, glucokinase showed maximum activity at pH 7.5 with g lucose-6-phosphate dehydrogenase as the coupling enzyme. In this assay , glucokinase was active with glucose (100%), 2-deoxy-D-glucose (40%), and mannose (20%). Partially purified glucokinase had a molecular wei ght of 82,000 and a pi of 4.82. Double-reciprocal plots of substrate c oncentration versus velocity were linear and the enzyme had apparent K -m values of 55 mu M for glucose and 72 mu M for GTP. Dialyzed cell ex tracts of Fibrobacter intestinalis C1A also contained a GTP-dependent glucokinase that showed little activity with ATP. Potassium also stimu lated the activity of this enzyme. These results suggest that this unu sual glucokinase may be characteristic of the genus Fibrobacter.