STUDIES ON MUSCLE DIFFERENTIATION. IV. ELECTROPHORETIC AND IMMUNOCHEMICAL ANALYSES OF TROPOMYOSIN FROM ADULT AND EMBRYONIC SKELETAL MUSCLES*, **

Tropomyosin preparations from skeletal muscles of the adult frog, chick and rabbit were resolved in 8 M urea-polyacrylamide gel electrophoresis into at least 5 to 6 components. Of these, main components clearly reacted with anti-frog tropomyosin antiserum in agar diffusion test. Especially, main components of the frog tropomyosin preparation contained both genus- and organ-specific and genus- and organ-nonspecific antigens without being differentiated into separate entities. The chick tropomyosin preparation formed a single band when thioglycolic acid was included in 8 M urea-polyacrylamide gel electrophoresis. This single component was revealed in an SDS-polyacrylamide gel electrophoresis to be monomeric tropomyosin subunit with a molecular weight of 34,000. Both adult and embryonic chick tropomyosin preparations in their course of purification were observed in 8 M urea-polyacrylamide gel electrophoresis to decrease in amount of the monomeric component with a concomitant increase in number and in amount of polymerized components. It was concluded that the monomeric subunit was the major form of tropomyosin molecules in both adult and embryonic skeletal muscle extracts of the chick and that the polymerized components with inter-subunit disulfide bonds were formed in the course of purification of the preparations.