Distribution of isoelectric variants of the 17,000-dalton myosin light chain in mammalian smooth muscle

D. J. Helper, J. A. Lash, D. R. Hathaway

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71 Scopus citations


Isoelectric focusing of purified vascular smooth muscle myosin revealed to variants of the 17,000-dalton light chain subunits. The isoelectric points of the light chain variants were determined to be 4.13 (LC(17a)) and 4.19 (LC(17b)). Tryptic peptide maps of the two species of light chain generated by reverse-phase high performance liquid chromatography disclosed small but obvious differences in peptide composition while amino acid analyses of the variants were quite similar. Two-dimensional electrophoresis of extracts from various mammalian smooth muscles revealed tissue-specific differences in the relative content of LC(17a) and LC(17b). Vascular (aorta, carotid, and pulmonary artery) muscles and tracheal smooth muscle contained both light chain variants while smooth muscle of the gastrointestinal tract (stomach and jejunum) contained LC(17a) only. The actin-activated Mg2+-ATPase activities of both phosphorylated and nonphosphorylated stomach (LC(17b) = 0) and aortic (LC(17b) = 40%) myosins were compared. In the presence of saturating tropomyosin, a 2-fold difference in V(max) was measured: phosphorylated, aortic, 0.119 ± 0.009 versus stomach, 0.239 ± 0.012 μmol of PO4 liberated/min/mg of myosin; non-phosphorylated, aortic, 0.065 ± 0.004 versus stomach, 0.123 ± 0.004 μmol of PO4 liberated/min/mg of myosin. In addition, the V(max) of myosin subfragment-1 ATPase from bovine aortic, pulmonary artery, and stomach myosins (LC(17b) contents, 40, 20, and 0%, respectively) was found to decrease in direct proportion to the LC(17b) content. Our results suggest that isoforms of the 17,000-dalton light chain subunits of mammalian smooth muscle myosin could play an important role in modulating actomyosin ATPase activity.

Original languageEnglish (US)
Pages (from-to)15748-15753
Number of pages6
JournalJournal of Biological Chemistry
Issue number30
StatePublished - Jan 1 1988

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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