Hasegawa Y, Morita F
Department of Chemistry, Faculty of Science, Hokkaido University.
J Biochem. 1992 Jun;111(6):804-9. doi: 10.1093/oxfordjournals.jbchem.a123840.
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)
主动脉平滑肌肌球蛋白包含两种17 kDa的必需轻链，即LC17nm（非肌肉型）和LC17gi（砂囊型）[长谷川洋、上田洋、渡边正、森田房夫（1992年），《生物化学杂志》111卷，798 - 803页]。通过在46℃孵育，LC17同工型从猪主动脉肌球蛋白中释放出来。LC17gi的释放速率比LC17nm高1.5至2倍。可以重构含有不同比例两种LC17同工型的主动脉肌球蛋白。测量肌动蛋白激活的ATP酶活性作为LC17nm含量的函数。含有更多LC17nm的肌球蛋白的Vm值较低。对于F - 肌动蛋白，含有81% LC17nm的肌球蛋白的表观解离常数Km比含有23% LC17nm的肌球蛋白低20倍。在腺苷酰亚胺二磷酸存在的情况下，观察到肌球蛋白与F - 肌动蛋白的解离常数有类似差异。LC17nm的作用似乎是使主动脉肌球蛋白适合以低能量消耗维持肌肉张力。肌球蛋白与F - 肌动蛋白结合亲和力的同工型依赖性差异似乎部分归因于LC17同工型自身与F - 肌动蛋白亲和力的差异。我们发现分离的LC17nm自身能够以64 microM的解离常数与F - 肌动蛋白结合，但LC17gi不能。（摘要截短至250字）
