Abstract
IT is now well established that myosins from vertebrate skeletal and smooth muscles possess a light chain component of 18,000 to 20,000 molecular weight, the P light chain, that can be phosphorylated by an enzyme present in sarcoplasm1–3. This enzyme, myosin light chain kinase, of molecular weight about 77,000 (ref. 4 and E. V. Pires and S.V.P., unpublished) is highly specific for the transfer of the γ phosphate of ATP to a single serine residue1 close to the N terminus of the P light chain5. Fully phosphorylated myosin therefore contains 2 mol covalently bound P mol−1 as two P light chains are present in each myosin molecule. Dephosphorylation of the P light chain is catalysed by an enzyme, myosin light chain phosphatase, that has recently been characterised6 and shown to be highly specific for the P light chain. Myosin light chain phosphatase has a molecular weight of 70,000 and is also present in the sarcoplasm. The presence of such a highly specific enzyme system for the phosphorylation and dephosphorylation of the P light chain strongly suggests a role in the physiological function of muscle. The amounts of the two enzymes present in skeletal muscle are such that it is unlikely that a complete cycle of phosphorylation and dephosphorylation of the P light chain can occur during a single twitch3,7; it could, however, take place within a matter of seconds. We report here that changes in the phosphorylation of the P light chain in the perfused rabbit heart can be correlated with changes in the physiological state of the muscle.
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FREARSON, N., SOLARO, R. & PERRY, S. Changes in phosphorylation of P light chain of myosin in perfused rabbit heart. Nature 264, 801–802 (1976). https://doi.org/10.1038/264801a0
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DOI: https://doi.org/10.1038/264801a0
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