Protein Catabolism in Rat Liver Homogenates

Abstract

Abstract Protein catabolic activity in rat liver preparations at several levels of tissue intactness has been studied with a variety of metabolic inhibitors. The previous reports that energy inhibitors also inhibit protein catabolism in a liver slice have been confirmed. Some of these same inhibitions, although reduced, were also observed in liver homogenates. However, the ability of several types of inhibitors, including energy or respiratory inhibitors, to inhibit protein catabolism is shown to be dependent on the level of tissue integrity while other inhibitions are not affected greatly by tissue integrity. Addition of carrier amino acid to the incubations is shown to facilitate equilibration with the incubation media containing labeled amino acids released from protein catabolism and the remaining protein, refuting earlier reports that the addition diluted out amino acids for reincorporation of the tracer into new protein. This new evidence requires a re-evaluation of the apparent energy requirement for protein catabolism. There may be a structural component involved in protein catabolism, the integrity of which requires metabolic energy, while the enzymes involved in the actual degradation of proteins probably do not have an energy requirement.