Ontogeny of chick liver hexokinase isozymes

Glucose phosphorylating activities were measured in liver extracts from chicks at several developmental stages. Enzyme activity levels in supernates were low (about 0.16 units/g liver) from day 10th of egg incubation until the 17th day, at which time a transient increase to 0.5 units/g was observed. At hatching, the levels were again low (0.15 units/g) compared to adult levels (0.9 units/g). Particulate hexokinase activity was rather constant from day 10th to adulthood (about 0.3 units/g). Chromatography of liver supernates in DEAE-cellulose columns revealed the presence of four hexokinases in embryos up to day 15th of incubation. From that day onwards, the least retained from (hexokinase 4) was no longer found. The most retained form (hexokinase 1) disappeared at hatching, at which time a pattern consisting of hexokinases 2 and 3 was found to be very similar to the adult profile. The four isozymes were characterized as low Km glucose hexokinase of broad sugar specificities and molecular weights of about 100,000. Particulate hexokinase activity of embryonic chick liver was found to be composed of the same isozymes observed in cytosolic extracts. Incubation of particles with glucose 6-P or ATP failed to release hexokinase activity.