Abstract

In the aquatic fungus Allomyces macrogynus the effects of Ca^2+ and cAMP on the intracellular signal transduction of zeoospore germination were studied using in vitro protein phosphorylation assay system. An endogenuously phosphorylated protein (p50) having molecular weight of 50 kDa on SDS-PAGE was found in soluble fractions of both zeoospore and mycelium. In zoospore extract, the endogenous phophorylation of p50 was weak without any effectors, but was enhanced by Ca^2+ and even more by cAMP. Phosphorylation of the same protein in mycelial extract was high only in the absence of cAMP. Irrespective of the presence of Ca^2+ and cAMP, its phosphorylation was antagonistically suppressed in assay of combined zoospore and mycelial extracts. These results suggest that p50 is interconvertible in phosphorylation/dephosphorylation as a novel protein involved in germination of A. macrogynus. The antagonistic effect of cAMP to the phosphorylation of p50s from different developmental stages may be important in the regulation of cellular differentiation.

• Keywords: Allomyces macrogynus; cellular differentiation; endogenous protein phosphorylation; cAMP; calcium ion