Study of Protein Synthesis in Rat Liver Mitochondria: Use of Cycloheximide

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Abstract
Effects of short-term and long-term administration of cycloheximide on rat liver mitochondrial protein synthesis were examined and were found to be different. Long-term administration of cycloheximide resulted in inhibition of total cellular protein synthesis including that of mitochondria while, a short-term intervals, 8-10% of mitochondrial protein synthesis was cycloheximide-resistant. The inhibitory effect was also reflected in terms of protein synthesizing ability of mitochondria in vitro, the inhibition becoming apparent at 40 min and showing progressive increase with time. The observed inhibition of mitochondrial protein synthesis by cycloheximide was not due to either inhibition of energy metabolism or alteration of amino-acid pool. Cycloheximide did not enter mitochondria or sonic preparation under conditions in vitro. After administration of [3H]cycloheximide, significant quantities of the label were found to be associated with mitochondria and mitoribosomes. Cycloheximide apparently reached the site of action in mitochondria under conditions in vivo but was unable to do so in vitro. Possible mechanisms involved in the inhibition of true mitochondrial protein synthesis by cycloheximide are discussed.