Reversible self-phosphorylation of asparaginase complex in Leptosphaeria michotii: characterization of associated protein kinase and protein phosphatase activities.

Regulation of the asparaginase activity rhythm in L. michotii has previously been shown to be dependent on a reversible phosphorylation process. Asparaginase was isolated as a purified protein complex having self-phosphorylating capacities, which were analyzed. In vivo phosphorylation of asparaginase complex was performed synchronously with the rhythm of asparaginase activity. In vitro self-phosphorylation of asparaginase complex resulted from the activity of an ATP-Mg2+-dependent protein kinase, which phosphorylated protein at threonine residues and was not dependent on cyclic AMP, Ca2+ or calmodulin. Dephosphorylation of this complex was due to a Mg2+-Zn2+-dependent protein phosphatase, molybdate inhibited, the specificity of which, for low-molecular-weight nonprotein phosphoesters, was broad.