Immunoquantitation of liver glucose-6-phosphate dehydrogenase and malic enzyme in normally and prematurely weaned rats

Rat liver glucose-6-phosphate dehydrogenase and malic enzyme were purified and rabbit serum antibodies were prepared against each enzyme. The activities and quantities of both enzymes in the livers of infant rats were subsequently determined during the weaning period. Glucose-6-phosphate dehydrogenase was present and active in the liver of spontaneously weaned rats on postnatal day 17 and increased from postnatal day 21 onwards. Malic enzyme and its activity were undetectable on postnatal day 17. The latter enzyme was detected on postnatal day 21 and increased rapidly afterwards. These changes occurred sooner and were more pronounced when the rats were weaned prematurely on postnatal day 17, especially when the diet contained sucrose. The activities of both enzymes were highly correlated with the amounts of enzyme protein present throughout the experiment. It appeared that the activities of both enzymes in infant rats were likely to be regulated by altering their synthesis and (or) degradation, rather than by activation of existing proteins, assuming that the latter can be detected by the antibodies employed.