Different Biochemical Properties of Foetal and Adult Red Cell Hexokinase Isoenzymes

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Abstract
The distribution of hexokinase isoenzymes was analyzed in erythrocytes from adults and newborn infants. Isolation by DEAE-cellulose chromatography revealed 1 main peak (Ia) in erythrocytes from adults similar to hexokinase isoenzyme I from rat liver and a smaller peak (Ib) which was eluted at a lower conductivity than rat liver isoenzyme II. In erythrocytes from newborn infants the peak Ib dominated, isoenzyme Ia was the smaller one. In adult erythrocytes an additional isoenzyme was detected which resembled rat liver isoenzyme III; this isoenzyme was absent in erythrocytes from newborn infants. The erythrocytic isoenzymes Ia and Ib differed in their kinetic properties. Isoenzyme Ia had a slightly higher affinity or glucose (Km 47 .mu.M) than isoenzyme Ib (Km 100 .mu.M). In the presence of 5 mM Pi isoenzyme Ib was more inhibited by glucose 6-phosphate than isoenzyme Ia. 2,3-Diphosphoglycerate inhibited isoenzyme Ib more than isoenzyme Ia.

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