Myosin from Striated Adductor Muscle of Chlamys nipponensis akazara

Abstract

Myosin was isolated from striated adductor muscle of Akazara shell-fish, and purified on DEAE-Sephadex A50. The sedimentation constant (s⁰₂₀, _w) and the intrinsic viscosity, [η] of Akazara myosin thus purified were estimated to be 6.6S and 2.10dl/g, respectively. In many respects, Akazara myosin was similar to scallop myosin. (1) Only one size of light-chain component (17, 000 daltons) was detectable in SDS-gel electrophoresis of Akazara myosin, but two types of light-chain component were seen in urea-gel electrophoresis; these were equivalent to EDTA-light chain and SH-light chain of scallop myosin. The molar ratio of heavy chain (206, 000 daltons), EDTA-light chain, and SH-light chain in Akazara myosin was estimated, from the staining densities of gel-electrophoretic bands, to be approximately 1:1:1. (2) The EDTA-washing procedure removed EDTA-light chain only, causing desensitization of Akazara myosin. EDTA-light chain isolated from Akazara myofibrils was able to resensitize EDTA-washed Akazara myosin.
Akazara myosin, however, was found to be different from scallop myosin in two important properties: (1) complete removal of EDTA-light chains was required to achieve a complete loss of calcium sensitivity, and full resensitization was attained on recombination of EDTA-light chains with desensitized myosin prepared essentially free from EDTA-light chains. (2) EDTA-light chains isolated from Akazara myofibrils show a calcium-induced UV absorption difference spectrum.