J. Biol. Chem., Vol. 259, Issue 6, 3475-3481, Mar, 1984
Monoclonal antibodies to rabbit skeletal muscle protein phosphatases C- I and C-II
M Speth, R Alejandro and EY Lee
Rabbit skeletal muscle protein phosphatases C-I and C-II have been
previously isolated as two proteins of Mr = approximately 35,000. Both
enzymes display broad substrate specificities but have distinct enzymatic
properties in regard to their susceptibility to heat-stable protein
inhibitor-2 and their response to divalent cations. Monoclonal antibodies
against both protein phosphatase C-I and C-II were produced by fusion of
spleen cells of immunized BALB/c mice with SP2/0-Ag14 mouse myeloma cells.
The products of the hybrid cells were screened by solid phase
radioimmunoassay for the production of antibodies to protein phosphatase
C-I and C-II. Positive cells were cloned and injected into mice to produce
ascitic fluids. Ten monoclonal antibodies against phosphatase C-I and eight
monoclonal antibodies against phosphatase C-II were obtained. These
antibodies were characterized with regard to their relative binding
affinities to the two protein phosphatases and their abilities to inhibit
the phosphorylase phosphatase activities of the two enzymes. All ten of the
phosphatase C- I monoclonal antibodies inhibited the phosphorylase
phosphatase activity of phosphatase C-I, and three of these also inhibited
phosphatase C-II. Only one of the eight antibodies to phosphatase C-II was
inhibitory and inhibited the activities of both phosphatase C-I and C-II.
Examination of the binding of these monoclonal antibodies by a solid phase
radioimmunoassay showed that eight of the ten phosphatase C- I antibodies
cross-reacted with phosphatase C-II, while all eight of the phosphatase
C-II antibodies cross-reacted with phosphatase C-I. These findings show
that phosphatases C-I and C-II possess common antigenic determinant(s) and
may, therefore, be structurally related proteins.