The Journal of Cell Biology, Vol 90, 408-414, Copyright © 1981 by The Rockefeller University Press
Hybrids of Physarum myosin light chains and desensitized scallop myofibrils
VT Nachmias
The two light chains of Physarum myosin have been purified in a 1:1 ratio
with a yield of 0.5-1 mg/100 g of plasmodium and a purity of 40- 70%; the
major contaminant is a 42,000-dalton protein. The 17,700 Mr Physarum myosin
light chain (PhLC1) binds to scallop myofibrils, providing the regulatory
light chains (ScRLC) have been removed. The 16,500 Mr light (PhLC2) does
not bind to scallop myofibrils. The calcium control of scallop myosin
ATPase is lost by the removal of one of the two ScRLC's and restored
equally well by the binding of either PhLC1 or rabbit skeletal myosin light
chains. When both ScRLC's are removed, replacement by two plasmodial light
chains does not restore calcium control as platelet or scallop light chains
do. Purified plasmodial actomyosin does not bind calcium in 10(-6) M free
calcium, 1 mM MgCl2. No tropomyosin was isolated from Physarum by standard
methods. Because the Physarum myosin light chains can substitute only
partially for light chains from myosin linked systems, because calcium does
not bind to the actomyosin, and because tropomyosin is apparently absent,
the regulation of plasmodial actomyosin by micromolar Ca++ may involve
other mechanisms, possibly phosphorylation.
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