A study on the kinetics and mechanism of D-lyxose and D-xylose activation of the adenosine triphosphatase activity associated with yeast hexokinase.

The activation of the ATPase activity of yeast hexokinase by D-lyxose and D-xylose was investigated. Sugars lacking a carbon 6 activate the ATPase activity while the presence of a carbon 6 inhibits the activity. Xylose and lyxose, which are competitive inhibitors of glucose in the hexokinase reaction, induce substrate inhibition by ATP in the hexokinase and ATPase reactions. Ultracentrifugation studies indicate that the various sugars change the conformation of hexokinase to give lower ~~0,~ values. The pentose activation of the ATPase activity has previously been interpreted as evidence for an ordered mechanism, but the initial rate and competitive inhibition studies of this report support a random addition of pentose and ATP in the reaction. These results are consistent with the proposed Random Bi Bi mechanism suggested for hexokinase.