Incorporation of amino acids into mitochondrial protein of the flight muscle of Locusta migratoria in vitro and in vivo in the presence of cycloheximide.

The incorporation of arnino acids into distinct protein fractions of mitochondria from various sources [1-4) including a cytoplasmic mutant of Neurospora crassa [5] has been shown tobe an inherent Capacity of isolated mitochondria in vitro. An independent method for studying this system is affered by the specific inhibition of extramitochondrial protein synthesis in vivo. Cycloheximide is known as a strong inhibitor of protein synthesis catalysed by microsomal ribosomes of higher organisms [ 6] . In contrast, protein synthesis in isolated mitochondria in vitro (3,5,7] similar to bacteria (8] is unaffected by the antibiotic. Some recent reports indicate furtherrnore that in vivo under the influence of cycloheximide, incorporation of arnino acids into mitochondrial proteins is inhibited to a smaller extent than incorporation into microsomal proteins [9]. In this communication we report experiments in vivo with the flight muscle of Locusta migra· toria. Under the influence of cycloheximide, amino acids are incorporated only into some fractions of electrophoretically separated mitochondrial proteins. The labelling pattern is very similar after incorporation in vitro, but clearly distinct in a control experiment in vivo without cycloheximide.