Manganese modulates protein phosphorylation in the rat pancreas: in vitro evidence for cation selective regulation

The effects of manganese (Mn2+) on phosphorylation activity in the rat pancreas were examined in an in vitro phosphorylation assay and by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of endogenous proteins. Several histones were phosphorylated in the presence of pancreatic supernatant obtained following a 10-min centrifugation at 15,000 g. The histone preference for this reaction was VII-S greater than V-S or II-S greater than III-S greater than other histones. The Mn2+ (10 mM) enhanced the phosphorylation of some histones (II-A, III-S, VI-S, and VIII-S) but inhibited the phosphorylation of other histones (II-S, V-S, and VII-S). The same concentration of Mn2+ also enhanced the incorporation of 32P into cytosolic proteins in the absence of exogenous histones. This effect was not mimicked by Ca2+, Mg2+, Ba2+, or Zn2+. Analysis of endogenous proteins by SDS-PAGE revealed Mn2(+)-dependent and time-dependent phosphorylation of high (98-200-kDa), intermediate (59-,52-,35-, and 30-kDa), and low-molecular weight proteins. The Mn2+ exerted similar effects in the presence of pancreatic cytosol obtained following a 60-min centrifugation at 100,000 g. However, the 35- and 30-kDa phosphoproteins and the low-molecular weight proteins were not readily visible. In both the 15,000- and the 100,000-g preparations, there was a dose-dependent increase in the phosphorylation of the Mr 98-kDa protein (p98) at concentrations ranging from 0.03 to 1.0 mM Mn2+ but a lesser stimulatory effect at 10.0 mM Mn2+.(ABSTRACT TRUNCATED AT 250 WORDS)