DEGRADATION OF PEROXISOMAL CATALASE IN AN NORMAL-ALKANE-UTILIZABLE YEAST, CANDIDA-TROPICALIS

A drastic decrease in the activities of peroxisomal enzymes, catalase and acyl-CoA oxidase, was observed when an n-alkane-assimilating yeast, Candida tropicalis, was transferred from an n-alkane medium into a glucose medium. The level of the activity of catalase, one of the peroxisomal enzymes inducibly synthesized in harmony with the development of peroxisomes, decreased parallelly with the disappearance of peroxisomes. Degradation of catalase in peroxisomes is suggested to consist of two processes as a result of the transfer experiments of cells in the presence and absence of cycloheximide. One is a process independent of protein synthesis de novo, while the other is a process dependent on protein synthesis de novo. Within 1 h after transfer, it was noticeable that the decrease in the level of mRNA encoding catalase occurred more drastically than that in the catalase activity. Western blot analysis using anti-catalase antiserum after subcellular fractionation demonstrated that degradation products of catalase were present in peroxisomes before and even after transfering cells from the alkane medium into the glucose medium. These facts suggest that peroxisomes might have a certain inherent system of proteolysis, related to the turnover of peroxisomal proteins, and that this system would continue to operate without protein synthesis de novo after rapid repression of the synthesis of mRNA encoding catalase. Finally, catalase seemed to be further degraded with proteases of vacuoles synthesized de novo, the catalase activity reaching a house-keeping level.