Abstract
It was found that cycloheximide injected into rats inhibited the incorporation of 14C-leucine into catalase in vivo, not affecting the concentration of catalase-synthesizing ribosomes and the amount of nascent catalase. The liver ribosomes of rats given cycloheximide by intraperitoneal injection incorporated less amino acids into catalase than the ribosomes from intact rat liver, when incubated in vitro with normal cell sap. The cell sap preparation from livers of cycloheximide-treated rats was also less active for catalase synthesis, and the activity could not be restored by treatment with Sephadex. It may be concluded that both the ribosomes and the cell sap are impaired by the treatment of rats with cycloheximide. At low concentration, cycloheximide added into the cell-free system inhibited the labeling of soluble catalase, but not that of catalase-synthesizing ribosomes and nascent catalase. The evidence suggests that the low concentration of cycloheximide interferes with the release of completed catalase molecules from the ribosomes without any effect on incorporation of 14C-leucine into nascent catalase. However, at higher concentrations, the labeling of catalase-synthesizing ribosomes and nascent catalase was decreased, as well as that of soluble catalase. A kinetic study also indicated that this antibiotic would inhibit elongation of nascent catalase on the ribosomes. From these findings, it has been concluded that cycloheximide inhibits the termination, the elongation and possibly the initiation in the course of catalase biosynthesis.
