Polyphosphate glucokinase from Propionibacterium shermanii. Kinetics and demonstration that the mechanism involves...

Polyphosphate glucokinase (EC 2.7.1.63, polyphosphate glucose phosphotransferase) has been partially purified (960-fold) from Propionibacterium shermanii. Throughout the purification, the ratio of polyphosphate glucokinase activity to ATP glucokinase activity remained approximately constant at 4 to 1. It is considered that both activities are catalyzed by the same protein. The mechanism of utilization of polyphosphate by polyphosphate glucokinase was investigated using polyphosphates of limited sizes that were isolated following gel electrophoresis of commercial heterogeneous polyphosphates. The results show that with long chain polyphosphates, the reaction proceeds by a processive type mechanism, and with short polyphosphates, it is nonprocessive. The Km for polyphosphate of chain length 724 is 2 X 10(-3) microM and increases with a decrease in chain length to 3.7 X 10(-2) microM at chain length 138. Subsequently, there is a very rapid increase of Km and at chain length 30 the Km is 4.3 microM. The rapid change in Km coincides with the shift in mechanism from the processive type mechanism in which there apparently is successive phosphorylation prior to release from the enzyme to a nonprocessive process in which the polyphosphate is released from the enzyme after each transfer. During the nonprocessive process, there is preferential utilization of the longer species. The Vmax is relatively constant with shorter polyphosphates but decreases with chain lengths longer than 347. In the cell, as a consequence of the low Km, the long chain polyphosphates probably are used preferentially to phosphorylate glucose.