SERINE THREONINE PROTEIN PHOSPHATASES AND A PROTEIN PHOSPHATASE-1 INHIBITOR FROM NEUROSPORA-CRASSA/

The major spontaneously active serine/threonine (Ser/Thr) protein phos phatase activities in N. crassa wild type (FGSC 424) were type-1 (pp1) , type-2A (PP2A) and type-2C (PP2C). PP1 and PP2C predominantly dephos phorylated phosphorylase a and casein, respectively. PP2A acted on bot h substrates, but was two-fold more active against casein. PP1 activit y was inhibited by protamine, heparin, okadaic acid (IC50 50 nM) and m ammalian inhibitor-1 (IC50 2 nM). On the other hand, PP2A activity was inhibited by much lower concentrations of okadaic acid (IC50 0 2 nM) and also by protamine, but not by heparin or inhibitor-1. About 80% of total PP1 activity was associated with the particulate fraction and c ould be partially extracted with 0.5 M NaCl. Seventy and ninety percen t of PP2A and PP2C activities, respectively, were found in the soluble fraction. In addition we have partially purified an acid and-thermost able PPI inhibitor which effectively inhibits both N. crassa and mamma lian PP1.