Role of 17-kDa essential light chain isoforms of aorta smooth muscle myosin.
Aorta smooth muscle myosin contains two kinds of 17-kDa essential light chain, LC17nm (nonmuscle-type) and LC17gi (gizzard-type) [Hasegawa, Y., Ueda, Y., Watanabe, M., & Morita, F. (1992) J. Biochem. 111, 798-803]. The LC17 isoforms were released from porcine aorta myosin by incubation at 46 degrees C. The rate of release was 1.5 to 2 times higher with LC17gi than with LC17nm. Aorta myosins containing the two LC17 isoforms in various ratios could be reconstituted. The actin-activated ATPase activity was measured as a function of LC17nm content. The Vm value was lower with myosin which contained more LC17nm. The apparent dissociation constant for F-actin, Km, was 20-fold less with myosin which contained 81% LC17nm than myosin which contained 23% LC17nm. A similar difference in the dissociation constants of myosin for F-actin was observed in the presence of adenylyl imidodiphosphate. The role of LC17nm appears to be to make aorta myosin suitable for maintaining the muscle tension with a low expenditure of energy. The isoform-dependent difference in the F-actin-binding affinities of myosin seems partly due to the difference in the affinities of LC17 isoforms themselves for F-actin. We found that the isolated LC17nm itself could bind with F-actin with a dissociation constant of 64 microM, but LC17gi could not.(ABSTRACT TRUNCATED AT 250 WORDS)
Hasegawa
Y
Y
Department of Chemistry, Faculty of Science, Hokkaido University.
Morita
F
F
D000199:Actins / Q000378:metabolism; D000266:Adenylyl Imidodiphosphate / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008970:Molecular Weight; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009218:Myosins / Q000737:chemistry / Q000378:metabolism*; D013552:Swine
D000199:Actins; D000266:Adenylyl Imidodiphosphate; D009218:Myosins