Vesiculation of the kidney microvillus membrane.

Thus dephosphorylation will increase during starvation as the ratio of dephosphorylating/phosphorylating activity increases by 4.5. Acute glucose loading alters this ratio to 1.5 times the fed value. Chicken liver hexokinases differ from rodent liver hexokinases in several important respects. No isoenzyme inhibited by high glucose concentrations is present in avian liver (Ureta et al., 1972), and we observed no inhibition of activity over a wide range of glucose concentrations. Inhibition of chicken liver hexokinases by N-acetylglucosamine had a K,,,/K, ratio of 0.22. This value is intermediate between tlle 0.02 of rat hexokinase and the 15 of rat glucokinase (Viiiuela et al., 1963). Thus there is no evidence for the presence of chicken glucokinase under normal nutritional conditions or under starvation plus acute glucose loading. The rate of glucose uptake and efflux from chicken liver is therefore likely to be regulated by substrate cycling involving glucose 6-phosphatase and hexokinase.