Protein synthesizing activity of chicken liver and muscle

Abstract

1. 1. Radioactivity incorporated in vivo into chicken liver proteins of the various cellular fractions was 4 to 5 times higher than that found in chicken muscle proteins of the corresponding cellular fractions when maximum radioactivity incorporated (per minute per mg. protein) into their respective proteins was compared. The specific radioactivity dropped by 52 to 75 % in the liver proteins and 22 to 30 % in the muscle proteins 96 hours after[ 3H]leucine administration. 2. 2. Amino acid incorporating activity of the post-mitochondrial (PM) fraction from chicken liver was 36 % of that a similar preparation from rat liver when chicken liver was homogenized in Tris-potassium-magnesium (TKM)-sucrose buffer and could be raised to 80 % by homogenizing in the presence of RNase inhibitor. PM fractions from the thigh muscles of the two animals showed similar activity although the activity was only 22 % of that of the rat liver preparation. 3. 3. Amino acid incorporating activity of the cell-free muscle preparation was 18% higher when the muscle was homogenized in the presence of 100 mM KCI and 16% lower when homogenized in the presence of 200 mM KCl compared to the amino acid incorporating activity of the preparation obtained by homogenizing the muscle in the presence of 25 mM KCl. 4. 4. The RNA concentration in chicken liver and thigh muscle was 6.92 and 2.05 mg. per g. of tissue and the lower amino acid incorporating activity of the muscle could be due to a lower RNA content in the tissue.