Cyclic activity of L‐asparaginase through reversible phosphorylation in Leptosphaeria michotii

Abstract

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.

Changes in protein kinase and protein phosphatase properties during the cycle of asparaginase activity in Leptosphaeria michotii

“…To explain the successive changes in protein kinase and protein phosphatase activities during the cycle of asparaginase activity in L. michotii, we propose that asparaginase, a tetramer whose subunits are never phosphorylated during the cycle of asparagina.se activity (Jerebzoff and Jerebzoff-Quintin 1984), is associated in the complex with one protein kinase and one protein phosphatase, the properties and phosphoryiation of which are continuously modified during the successive steps of the cycle of asparaginase activity. Two such modifications could be considered.…”

“…, f ^ ,• transferase isofomn through translation of its mRNA introauction (Romestant et al 1990), the other the rhythm of asparagi-In the fungus Leptosphaeria michotii (West) Sacc, two nase, this enzyme being obtained as a purifted cytosolic processes are involved in the control of the oscillating protein complex having protein kinase and protein phospattem of the asparagine-pyruvate pathway, one regu-phatase activities (Jerebzoff and Jerebzoff-Quintin 1984). lating the rhythm of the mitochondriai aspartate amino-This complex is auto-phosphorylated at threonine re-sidues in the presence of [7-'-P]-ATP-Mg-*.…”

“…So, the same molecule can exhibit primarily a protein phosphatase or an alkaline phosphatase activity, according to the phase of the asparaginase activity rhythm (Jerebzoff-Quintin and Jerebzoff 1986). Asparaginase subunits are never phosphorylated during the cycle of asparaginase activity (Jerebzoff and Jerebzoff-Quintin 1984). Moreover, the in vivo phosphorylation of the asparaginase complex is synchronous with the rhythm of asparaginase activity (Jerebzoff-Quintin and Jerebzoff 1986).…”