The Journal of Cell Biology, Vol 96, 1761-1765, Copyright © 1983 by The Rockefeller University Press
A 72,000-mol-wt protein from tomato inhibits rabbit acto-S-1 ATPase activity
M Vahey
Tomato activation inhibiting protein (AIP) is a molecule of an apparent
molecular weight of 72,000 that co-purifies with tomato actin. In an assay
system containing rabbit skeletal muscle F-actin and rabbit skeletal muscle
myosin subfragment-1 (myosin S-1), tomato AIP dissociated the acto-S-1
complex in the absence of Mg+2ATP and inhibited the ability of F-actin to
activate the low ionic strength Mg+2ATPase activity of myosin S-1. At a
molar ratio of 5 actin to 1 AIP, a 50% inhibition of the actin-activated
Mg+2ATPase activity of myosin S-1 was observed. The inhibition can be
reversed by raising the calcium ion concentration to 1 X 10(-5) M. The AIP
had no effect on the basal low ionic strength Mg+2ATPase activity of myosin
S-1 in the absence of actin. The protein did not bind directly to actin nor
did it cause depolymerization or aggregation of F-actin but appeared,
instead, to interact with the actin binding site on myosin S-1. Since AIP
is a potent, reversible inhibitor of the rabbit acto-S-1 ATPase activity,
it is postulated that it may be responsible for the low levels of actin
activation exhibited by tomato F-actin fractions containing the AIP.
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