Modulation of the substrate specificity of the polycation‐stimulated protein phosphatase from Xenopus laevis oocytes

Abstract

A polycation‐stimulated (PCS) protein phosphatase was isolated in high yield (280 μg/100 g ovaries) from Xenopus laevis oocytes through a procedure involving a tyrosine‐agarose hydrophobic chromatography. The 220‐kDa enzyme contains a 35‐kDa and a 62‐kDa subunit. It was identified as the low‐Mr polycation‐stimulated (PCSL) protein phosphatase. The labile p‐nitrophenyl phosphatase activity, copurifying with the phosphorylase phosphatase activity, can be increased severalfold by preincubating the purified enzyme with ATP, its analogues or PPi. This activation is time‐dependent and accompanied by a parallel decrease of the phosphorylase phosphatase activity. Although the stimulation was antagonized by metal ions during the preincubation, the basal and ATP‐stimulated p‐nitrophenyl phosphatase requires Mg2+ or Mn2+ in the assay, with pH optima of 8.5–9 and 7.5 respectively. Copyright © 1988, Wiley Blackwell. All rights reserved