In the insulin producing cell line RINm5F distribution of serine/threo
nine specific protein phosphatases type 1 (PPI) and 2A (PP2A) was stud
ied. Using different agents which inhibit or stimulate PPI and PP2A we
found that in membrane and nuclear fractions phosphatase activity was
inhibited by okadaic acid (OA), protamine, heparin, and inhibitor-2 i
n a concentration-dependent manner. C-2-ceramide had no effect. In the
cytosolic fraction the inhibitory effect of okadaic acid was tenfold
higher. Protamine stimulated phosphatase activity at low concentration
s and became inhibitory at higher concentrations. Inhibitor-2 and hepa
rin caused a decrease in phosphatase activity whereas C-2-ceramide led
to a slight activation. The data suggest that in membrane and nuclear
fractions of RINm5F cells predominantly PPI is present, whereas in th
e cytosol PPI as well as PP2A can be detected. (C) 1998 Elsevier Scien
ce B.V. All rights reserved.