Abstract
Monoclonal antibodies against gizzard smooth muscle myosin were generated and characterized. One of these antibodies, designated MM-2, recognized the 17-kDa light chain and modulated the ATPase activities and hydrodynamic properties of smooth muscle myosin. Rotary shadowing electron microscopy showed that MM-2 binds 51 (+/- 25) A from the head-rod junction. The depression of Ca2+- and Mg2+-ATPase activities of myosin and Ca2+-ATPase activity of heavy meromyosin at low KCl concentration were abolished by MM-2. Viscosity measurement indicated that MM-2 inhibits the transition of 6 S myosin to 10 S myosin. While the rate of the production of subfragment-1 by papain proteolysis of 6 S myosin was inhibited by MM-2, the rate of proteolysis of the heavy chain of 10 S myosin was enhanced by MM-2 and reached the same rate as that of 6 S myosin plus MM-2. These results suggest that MM-2 inhibits the formation of 10 S myosin by binding to the 17-kDa light chain which is localized at the head-neck region of the myosin molecule. MM-2 increased the Vmax of actin-activated Mg2+-ATPase activities of both dephosphorylated myosin and dephosphorylated heavy meromyosin about 10- and 20-fold, respectively. MM-2 also activated the actin-activated Mg2+-ATPase activity of phosphorylated myosin at a low MgCl2 concentration and thus abolished the Mg2+-dependence of acto phosphorylated myosin ATPase activity. These results suggest that MM-2 inhibits the formation of 10 S myosin, and this results in the activation of actin-activated Mg2+-ATPase activity even in the absence of phosphorylation.
Highlights
From the $Department of Physiologyand Biophysics, CaseWestern Reserve University,Ckueland, Ohio 44106 and the UDepartment of Cell Biology, University of Massachusetts Medical School, Worcester,Massachusetts 01605
Monoclonal antibodies against gizzard smooth mus- the conformational transition, the most important finding is cle myosin were generated and characterized
Monova- was shown that the MF-ATPaseactivity of smooth muscle lent fragments of "-2 obtained by trypsin digestion
Summary
From the $Department of Physiologyand Biophysics, CaseWestern Reserve University,Ckueland, Ohio 44106 and the UDepartment of Cell Biology, University of Massachusetts Medical School, Worcester,Massachusetts 01605. As reported previously (Ikebe and Hartshorne, 1985b),the level of actinactivated Mg2"ATPase activity of phosphorylated myosin is markedly dependent on the MgClz concentration.
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