The influence of Mg2+ on the phosphorylation and dephosphorylation of myosin by an actomyosin preparation from vascular smooth muscle |
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Authors: | R S Moreland G D Ford |
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Institution: | Department of Physiology, Medical College of Virginia Health Sciences Division, Virginia Commonwealth University Richmond, Virginia 23298 USA |
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Abstract: | Previous work has shown that Mg2+ levels modulate the net level of myosin light chain phosphorylation in bovine aortic smooth muscle actomyosin preparations. The goal of this study was to determine the precise step, i.e. phosphorylation or dephosphorylation, where Mg2+ modulates the net phosphorylation reaction. The technique using γ35S]ATPγS to monitor the phosphorylating step yielded no effect of either Mg2+ or Ca2+. Unfortunately the lack of Ca2+-dependence did not allow conclusions about the influence of Mg2+ on myosin light chain kinase activity. The study of the effect of Mg2+ on dephosphorylation showed that phosphatase activity in the actomyosin preparation exhibited a Mg2+ modulation only when the actomyosin was previously exposed to activating levels (3×10?5M) of Ca2+, suggesting the presence of a Ca2+ -regulation system for myosin light chain phosphatase. |
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