JBC, Vol. 251, Issue 5, 1247-1252, Mar, 1976
Quaternary structure of (Na+ + K+)-dependent adenosine triphosphatase
G. J. Giotta
(Na+ + K+)-dependent adenosine triphosphatase (NaK-ATPase) consists of two
polypeptide chains, a large polypeptide with a molecular weight of about
100,000, and a sialoglycoprotein with a molecular weight of about 40,000.
Cross-linking of purified NaK-ATPase with the (o-phenanthroline)2-cupric
ion complex (CP) results in the reversible formation of dimers, trimers,
tetramers, and pentamers of the large polypeptide and loss of NaK-ATPase
activity. ATPase activity is partially recovered if NaK-ATPase is incubated
with beta-mercaptoethanol after treatment with CP. In contrast to these
results, if NaK-ATPase is cross-linked in crude canine kidney microsomes,
only a dimer of the large polypeptide is formed. No cross-linking of the
sialoglycoprotein to the large polypeptide is detected when NaK-ATPase is
cross-linked in purified form. However, when NaK-ATPase is reacted with CP
in either purified or microsomal form, the sialoglycoprotein cross-links to
itself yielding a high molecular weight aggregate. The results show that
the functional subunit structure of NaK-ATPase consists of at least two
large polypeptides.