COOPERATIVE ACTIVATION OF MYOSIN BY LIGHT CHAIN PHOSPHORYLATION IN PERMEABILIZED SMOOTH-MUSCLE

被引:59
作者
VYAS, TB [1 ]
MOOERS, SU [1 ]
NARAYAN, SR [1 ]
WITHERELL, JC [1 ]
SIEGMAN, MJ [1 ]
BUTLER, TM [1 ]
机构
[1] THOMAS JEFFERSON UNIV,JEFFERSON MED COLL,DEPT PHYSIOL,PHILADELPHIA,PA 19107
来源
AMERICAN JOURNAL OF PHYSIOLOGY | 1992年 / 263卷 / 01期
关键词
REGULATION; ADENOSINE-TRIPHOSPHATASE; CONTRACTION;
D O I
10.1152/ajpcell.1992.263.1.C210
中图分类号
Q4 [生理学];
学科分类号
071003 ;
摘要
The purpose of this study was to determine the quantitative relationship between the number of myosin molecules that increase their ATPase activity and the degree of myosin light chain phosphorylation in smooth muscle. Single turnover experiments on the nucleotide bound to myosin were performed in the permeabilized rabbit portal vein. In the resting muscle, the rate of exchange of bound nucleoside diphosphate was biphasic and complete in approximately 30 min. When approximately 80% of the myosin light chain was thiophosphorylated, the nucleoside diphosphate exchange occurred at a much faster rate and was almost complete in 2 min. Thiophosphorylation of 10% of the myosin light chains caused an increase in the rate of ADP exchange from much more than 10% of the myosin subfragment-1. Less than 20% thiophosphorylation of the total myosin light chains resulted in the maximum increase in ADP exchanged in 2 min. It appears that a small degree of myosin light chain phosphorylation cooperatively turns on the maximum number of myosin molecules. Interestingly, even though <20% thiophosphorylation of the myosin light chain caused the maximum exchange of ADP within 2 min, higher degrees of thiophosphorylation were associated with further increases in the ATPase rates. We conclude that a small degree of myosin light chain thiophosphorylation cooperatively activates the maximum number of myosin molecules, and a higher degree of thiophosphorylation makes the myosin cycle faster. A kinetic model is proposed in which the rate constant for attachment of unphosphorylated cross bridges varies as a function of myosin light chain phosphorylation.
引用
收藏
页码:C210 / C219
页数:10
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