Thiophosphorylation independently activates each head of smooth
muscle myosin in vitro.
Harris, David E., Christopher J. Stromski, Eric Hayes & David M.
Warshaw.
Department of Molecular Physiology & Biophysics, University of
Vermont, Burlington, Vermont 05405
APStracts 2:0185C, 1995.
To determine if thiophosphorylation of the 20 kDa myosin light chain
activates each head of smooth muscle myosin independently of the head
with which it is paired, chicken gizzard smooth muscle myosin was
randomly thiophosphorylated, producing a mixture of un-, singly and
doubly thiophosphorylated myosin. Thiophosphorylation levels were
measured by glycerol/urea gels and the activity of this myosin was
determined by actin-activated ATPase measurements and in an in vitro
motility assay where the velocity of actin filaments moving over a
myosin coated surface is measured. Activity at each
thiophosphorylation level was similar to that previously observed for
mixtures of un- and doubly thiophosphorylated myosin (5). All doubly
thiophosphorylated myosin was then formed into filaments and removed
from randomly thiophosphorylated myosin by centrifugation. The
remaining myosin (mixture of un- and singly phosphorylated myosin),
which could not polymerize due to their conformation, retained nearly
equal to 70% activity compared to mixtures of un- and doubly
thiophosphorylated myosin. Thus, a thiophosphorylated smooth muscle
myosin head can produce substantial biochemical and mechanical
activity even when paired with an unphosphorylated partner.
Received 10 January 1995; accepted in final form 27 April 1995.
APS Manuscript Number C23-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 9 May 1995.