Comparison of the synthesis of the light and heavy chains of adult skeletal myosin

Abstract

1. Incorporation of amino acid into light chains and heavy chains of skeletal myosin has been studied by injection of radioactive leucine into adult rabbits. Light and heavy chain fractions were prepared by dissociation of myosin in 5 M guanidine hydrochloride. Three distinct polypeptide chain species were separated by chromatography on DEAE-Sephadex A-25 with molecular weights of 23 000 (light chain 1), 16 000 (light chain 2) and 12 000 (light chain 3) as determined by sodium dodecyl sulfate-acrylamide gel electrophoresis. 2. The specific activities of myosin light and heavy chains 30 min and 4 h after injection were about 20 and 60 %, respectively, of the values at 24 h. 3. Differences in pool sizes of myosin chains were evaluated by comparing the ratio of specific activities of chains at different times after labeling, since polypeptide chains with larger pools would be expected to become labeled more slowly. The ratio of light chains to heavy chains after 30 min was smaller than after 4 and 24 h, suggesting that the pool of uncombined light chains is larger than that of uncombined heavy chains. 4. Following 4- and 24-h labeling periods the ratio of light chain 1 to heavy chain specific activities was about 0.7, light chain 2 to heavy chain 1.1, and light chain 3 to heavy chain 1.8. It is concluded that these differences in radioactive leucine incorporation after longer labeling periods probably reflect actual differences in synthesis of myosin chains.