Atypical Pattern of Utilization of Amino Acids for Mitochondrial Protein Synthesis in HeLa Cells

The capacity of HeLa cell mitochondria, either isolated or in intact cells, to incorporate different labeled amino acids into proteins was investigated. Eight amino acids (alanine, arginine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, and lysine), which include most of the charged polar ones, showed a very low amount, if any at all, of chloramphenicol-sensitive incorporation, relative to that expected for an "average" HeLa-cell protein. By contrast, the most hydrophobic amino acids (leucine, isoleucine, valine, phenylalanine, and methionine) were the most actively incorporated by HeLa mitochondria. The available evidence suggests that pool effects cannot account for this general pattern of utilization of amino acids; furthermore, this pattern is in good agreement with the known hydrophobic properties of proteins synthesized in mitochondria.