Cyclic AMP-dependent phosphorylation of proteins in mycelia of Rhizoctonia solani forming sclerotia.

Abstract

The phosphorylation of three cellular proteins from mycelia of Rhizoctonia solani was stimulated in the presence of adenylate 3', 5'-cyclic monophosphate (cAMP). The molecular weights of these proteins were determined to be 25, 000, 32, 000 and 62, 000 by gel electrophoresis in the presence of SDS. One of them (62K protein) was phosphorylated in the presence of cAMP to the maximal level within 5min, and the ATP concentration was saturated for the phosphorylation of this protein at 20μM. The Ka value for cAMP in the phosphorylation of 62K protein was approximately 0.1μM. NAD-dependent glutamate dehydrogenase activities in crude extracts of R. solani mycelia that form sclerotia in the presence of cAMP were inhibited significantly by preincubation with both ATP and cAMP. The inhibition of this enzyme activity saturated at 20μM ATP. The Ki value for cAMP on the inhibition of NAD-dependent glutamate dehydrogenase activity was approximately 0.1μM. These results suggest that inhibition of NAD-dependent glutamate dehydrogenase in R. solani mycelia is regulated by phosphorylation through activation of cAMP-dependent protein kinase.