This study demonstrates that the catalytic subunit of smooth muscle myosin phosphatase determines site specificity for dephosphorylation on the 20 kDa myosin light chain, while noncatalytic subunits enhance its activity.
Myosin phosphatase catalytic subunit confers MLC20 site specificity; extends basic mechanisms but leaves open physiologic relevance in cardiovascular disease.
The dephosphorylation of the myosin light chain kinase and protein kinase C sites on the 20 kDa myosin light chain by myosin phosphatase was investigated. The myosin phosphatase holoenzyme and catalytic subunit, dephosphorylated Ser-19, Thr-18 and Thr-9, but not Ser-1/Ser-2. The role of noncatalytic subunits in myosin phosphatase was to activate the phosphatase activity. For Ser-19 and Thr-18, this was due to a decrease in Km and an increase in k(cat) and for Thr-9 to a decrease in Km. Thus, the distinction between the various sites is a property of the catalytic subunit.
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Feng et al. (1999) studied this question.
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