JBC, Vol. 250, Issue 16, 6282-6287, Aug, 1975
The binding of divalent cations to myosin
M. C. Beinfeld, D. A. Bryce, D. Kochavy and A. Martonosi
Centrifuge transport, equilibrium dialysis, and electron paramagnetic
resonance studies on the binding of Mn2+ to myosin revealed two sets of
noninteracting binding sites which are characterized at low ionic strength
(0.016 M KCl) by affinity constants of 10(6) M-1 (Class I) and 10(3) M-1
(Class II), respectively. At 0.6 M KCl concentration, the affinity of Mn2+
for both sets of sites is reduced. The maximum number of binding sites is 2
for the high affinity and 20 to 25 for the low affinity set. Other divalent
metal ions displace Mn2+ from the high affinity sites in the following
order of effectiveness: Ca greater than Mg = Zn = Co greater than Sr
greater than Ni. The inhibitory effects of Mg2+ and Ca2+ upon the Mn2+
binding are competitive with inhibitor constants of 0.75 to 1 mM which is
similar to that of the low affinity divalent metal ion binding sites.
Exposure of myosin to 37 degrees partially inhibits Mn2+ binding to Class I
parallel with inhibition of ATPase activity. The binding of Mn2+ to the
high affinity binding sites is not significantly influenced by ADP or PPi,
although Mn2+ increases the affinity of ADP binding to myosin at high ionic
strength.
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