A novel thick filament protein in smooth muscles of bivalve molluscs

High-molecular-mass, heat-stable, resistant to organic solvents, water-inso luble and susceptible to proteolytic digestion protein has been found in 20 out of 24 muscles of seven bivalve mollusc species. As judged from SDS-PAG E data, the molecular mass of the protein polypeptide chains is 110-130 kDa , and its content in muscles 5-6%. The protein is localized in thick filame nts and can be removed together with myosin under conditions which left the paramyosin core undissolved. This protein is common in crude preparations of paramyosin and myosin. It is present in smooth muscles and absent in str iated and obliquely striated muscles. Its content in catch muscles is highe r than in non-catch or presumed non-catch muscles. (C) 1999 Elsevier Scienc e Inc. All rights reserved.