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-M r aggregate with asparaginase activity was phosphorylated by [γ-32P]ATP. By SDS-electrophoresis of dephosphorylated asparaginase a ∼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.
