Isolation and Characterization of Chloroform‐Soluble Proteins from Rat‐Liver Mitochondria and Other Fractions

Chloroform‐soluble proteins have been isolated free from phosphatides from rat liver mitochondria, microsomes and cytosol by chromatography on Sephadex LH‐20 columns. The amino acid composition of the chloroform‐soluble and insoluble proteins has been estimated. The chloroform‐soluble proteins from mitochondria and cytosol have a higher content of hydrophobic and a lower content of acidic amino acids compared to the corresponding chloroform‐insoluble proteins. No marked differences were found between chloroform‐soluble and insoluble proteins from microsomes. In contrast to the acidic chloroform‐insoluble proteins, all chloroform‐soluble proteins are basic. From the amino acid composition the amount of chloroform‐soluble proteins has been estimated. Mitochondrial membranes contain 1.6%, mitochondrial matrix proteins less than 0.025%, microsomes 3.0% and the cytosol 0.15% from total proteins. The molecular weight distribution of chloroform‐soluble proteins synthesized in mitochondria has been measured by gelelectrophoresis. The molecular weights range from about 7000 to 30000. The turnover of chloroform‐soluble proteins from mitochondria and cytosol is higher than from the corresponding chloroform‐insoluble proteins. A part of mitochondrial chloroform‐soluble proteins (about 30%) is synthesized within the mitochondria.