Reexamination of the conformation of muscle proteins by optical activity

The circular dichroism and optical rotatory dispersion of muscle proteins are reexamined. By the method of Chen et al. (Chen, Y.H., Yang, J.T., and Chau, K.H. (1974), Biochemistry 13, 3350), the estimated helical contents of myosin (78%), heavy meromyosin (HMM) (70%) subfragment 1 (SF-1) (60%), and G-actin (45%) are higher than hitherto reported. Tropomyosin (TM) and light meromyosin fraction I (LMM Fr. I) possess more than 90% helix in agreement with the values based on the bo method. HMM, SF-1, and G-actin also contain about 8, 16, and 27% beta form. The three troponins (TN) and three light chains (LC) of myosin have moderate amounts of helices (29 to 51%) and some beta form (13 to 23%). If the light chains are intact in HMM and SF-1, myosin would have 3-5% beta form, which is difficult to detect with the present method. For comparison, the predictive method based on amino acid sequence gives similar estimates for TM, G-actin, and TN-C with bound calcium, but slightly higher helical contents than our results for TN-I and the light chains.