The fractionation of proteins from ox-heart mitochondria labelled in vitro with radioactive amino acids

Abstract

Mitochondria labelled by incubation with radioactive amino acids were ultrasonically disrupted and fractionated by differential centrifugation, fractional precipitation with ethanol, chromatography on triethylaminoethylcellulose and density-equilibrium centrifugation. Very slight incorporation of amino acids was found into the proteins of the phosphorylating electron-transport particle. Relatively high incorporation of amino acids was found into proteins soluble in 50% (v/v) ethanol, and in a protein fraction slightly less dense than most of the mitochondrial proteins. It is concluded that the chief site of incorporation of amino acids is a relatively non-polar protein, possibly a lipoprotein, and the implications of this are discussed.