J. Biol. Chem., Vol. 261, Issue 20, 9222-9227, Jul, 1986
Purification of N-ethylmaleimide-sensitive ATPase from chromaffin granule membranes
S Cidon and N Nelson
An N-ethylmaleimide-sensitive ATPase was purified 100-fold from chromaffin
granule membranes. The purification procedure included solubilization with
polyoxyethylene 9 lauryl ether, chromatography on hydroxylapatite and
DEAE-cellulose columns, and glycerol gradient centrifugations. Inclusion of
phosphatidylserine and a mixture of protease inhibitors during the
purification procedure was necessary to maintain the activity of the
preparation. The purified preparation contained four major polypeptides
with molecular masses of about 115, 72, 57, and 39 kDa, which were
copurified with the ATPase activity. The 115-kDa subunit binds
[14C]dicyclohexylcarbodiimide and the subunits of 115 and 39 kDa bind
[14C]N-ethylmaleimide. The ATP-dependent proton uptake activity of
chromaffin granule membranes is inhibited 50% with about 20 microM
N-ethylmaleimide, while over 5 mM concentrations of the inhibitor were
required to block the ATPase activity of the membranes. The ATPase activity
of the purified enzyme was inhibited via two different affinities: a high
affinity site with a Ki in the microM range and a low affinity site in the
mM range, each contributing to about 50% inhibition of the enzyme. It is
concluded that the proton- ATPase of chromaffin granule membranes contains
at least four subunits with the 115-kDa polypeptide being the main subunit
having the active site for the ATPase activity of the enzyme.