Exchange of 20-kDa myosin light chain-bound phosphate during sustained contraction of arterial smooth muscle.
K(+)-contracted porcine carotid arterial muscles containing phosphorylated 20-kDa myosin light chains (LC) were exposed to carrier-free [32P]orthophosphate in K(+)-stimulating solution during sustained contraction. The covalently bound LC phosphate was completely replaced by [32P]phosphate, indicating that myosin light chain phosphatase and kinase have ready access to the bound phosphate during the sustained contraction. On average, 0.38 mol [32P]phosphate was incorporated per mole LC during the sustained K+ contraction. This value was about half of the maximal value for [32P]phosphate incorporation into LC, 0.74 mol/mol, in muscles contracted with K+ for 1 min. Assuming that sustained contraction involves the maximal number of cross-bridges attached to actin, the data suggest that half of the attached cross-bridges contain phosphorylated LC.
Bárány
M
M
Department of Biochemistry, College of Medicine, University of Illinois, Chicago 60612.
Rokolya
A
A
Bárány
K
K
D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D066298:In Vitro Techniques; D007700:Kinetics; D009119:Muscle Contraction; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism*; D009943:Organophosphorus Compounds / Q000378:metabolism*; D013552:Swine
D009943:Organophosphorus Compounds; D009218:Myosins