Similarities in properties,content, and relative rates of synthesis of fructose-P2 aldolase in livers of fed and starved rats

The present work gives evidence that, in contrast to the situation reported by Pontremoli et al. for the rabbit (Proc. Natl. Acad. Sci. U.S.A. 76, 6323–6325, 1979; Arch. Biochem. Biophys. 203, 390–394, 1980; Proc. Natl. Acad. Sci. U.S.A., 79, 5194–5196, 1992), starvation for as long as 3 days does not cause intracellular covalent modification and inactivation of fructose-P₂ aldolase molecules in rat liver cells. This conclusion is based on our observations that liver aldolase molecules isolated from fed and starved rats in the presence of proteolytic inhibitors were not distinguished on the basis of specific catalytic activity, electrophoretic mobility, subunit molecular weight, NH₂-terminat structure, or COOH-terminal structure. Further, the approximate 40% loss in rat liver mass which occurred during the 3-day fast was not associated with appreciable changes in the content of aldolase and most other abundant cytosolic proteinsper gram of rat liver, as judged by electrophoretic analysis of 100 000-g soluble fractions of liver extracts . Finally, a 3-day fast had no appreciable effect on therelative rates of synthesis of aldolase and most other abundant cytosolic proteins in rat liver. Our findings suggest that nutrient deprivation has no preferential effect on the concentration or metabolism of aldolase in rat liver cells.