Myosin may stay in EADP species during the catch contraction in scallop smooth muscle.
Myosin (opaque myosin) isolated from the opaque portion of scallop smooth muscle, a catch muscle, was subjected to limited digestion by trypsin during the steady-state ATPase reaction. The 200-kDa heavy chain of opaque myosin was cleaved into 125- and 74-kDa fragments. The proteolytic rate in the absence of Ca2+ was lower than that in the presence of Ca2+, and was similar to that in the presence of ADP and absence of Ca2+. The results suggest that the steady-state intermediate of opaque myosin ATPase in the absence of Ca2+ is EADP, which is consistent with the previous results based on the difference UV-absorption spectrum (Takahashi, M., Sohma, H., & Morita, F. (1988) J. Biochem. 104, 102-107). In the presence of F-actin, the proteolytic rates were decreased, but the digestive patterns by trypsin were similar to those of myosin alone. Even in the presence of F-actin, the proteolytic rate during the ATPase reaction in the absence of Ca2+ was lower than that in the presence of Ca2+, and was similar to that in the presence of ADP and absence of Ca2+. In addition, there was another trypsin-susceptible site which is probably located at 18 kDa from the N-terminal of the heavy chain. The site in the absence of Ca2+ was hardly cleaved when ATP or ADP was present. Similar tendencies were observed even in the presence of F-actin. These findings suggest that the intermediate of opaque myosin ATPase at the steady state in the absence of Ca2+ is EADP even in the presence of F-actin.(ABSTRACT TRUNCATED AT 250 WORDS)
Takahashi
M
M
Department of Chemistry, Faculty of Science, Hokkaido University.
Morita
F
F
D000199:Actins / Q000502:physiology; D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000502:physiology; D008974:Mollusca / Q000378:metabolism*; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000378:metabolism* / Q000502:physiology; D009218:Myosins / Q000378:metabolism*; D010766:Phosphorylation; D014357:Trypsin
D000199:Actins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D014357:Trypsin; D009218:Myosins; D002118:Calcium