Properties of pig mature erythrocyte hexokinase.

Previous studies have demonstrated the presence of two type III hexokinase isozymes in pig mature erythrocytes. The prevalence of a specific isozyme species is an age-dependent phenomenon. The mature erythrocyte of young adult pigs (less than 6 mo old) possess an isozyme that has an apparent Km for glucose that is lower than in adult pigs. The data in this report suggest several basic differences between the two isozymes. D-Mannoheptulose, a structural analogue of glucose, was observed to differentially inhibit the isozymes. The young adult isozyme tended to be heat sensitive when compared with adult isozymes. Carboxypeptidase B and trypsin inhibited the activity of both isozymes, but the young adult isozyme was most dramatically affected by carboxypeptidase B. When the two isozymes were incubated in the presence of two sulfhydryl group inhibitors, HgCl2 and 5,5'-dithiobis [2-nitrobenzoic acid] (DTNB), the young adult isozyme exhibited the greater inhibition in the presence of DTNB. The data suggest that the young adult isozyme exhibited pronounced differences in activity when incubated in the presence of DTNB and carboxypeptidase B. These two agents may be used as probes to further characterize the properties of the two isozymes.