Cyclic activity of L-asparaginase through reversible phosphorylation in Leptosphaeria michotii.

Asparaginase in L. michotii has previously been shown to have an activity rhythm, the mechanisms of which were investigated. In vitro activation, or reactivation after dephosphorylation, of the partially (200-fold) purified asparaginase with protein kinase activity was obtained by ATP or Pi addition; these effects varied according to the phase of the activity rhythm at which enzyme was extracted. A high-Mr aggregate with asparaginase activity was phosphorylated by [gamma-32P]ATP. By SDS-electrophoresis of dephosphorylated asparaginase a approximately 60-kDa 32P-labelled protein with alkaline phosphatase activity became detectable. Regulation of the asparaginase activity rhythm in L. michotii is dependent on a reversible phosphorylation process.