Regulation of the cyclic activity of asparaginase (obtained as a purified protein complex) by a reversible auto‐phosphorylation process has been previously reported in the fungusLeptosphaeria michotii(West) Sacc.In the present study, the protein complex was purified in the presence of either a mixture of 3 protein phosphatase inhibitors (fluoride, vanadate and molybdate) or EGTA, during the cycle of asparaginase activity, and the protein kinase and protein phosphatase activities characterized. (I) At the phase of increasing asparaginase activity, a Ca2+/calmodulin‐dependent kinase activity was identified by (a) its inhibition by calmidazolium, reversed by calmodulin, and its inhibition by EGTA, but not by poly(Glu/Tyr 4:1)n. dichloro‐(ribofuranosyl)‐benzimidazole or polylysine (b) an increasing level of calmodulin bound to the complex, as estimated by enzyme‐linked immunosorbent assay (ELISA). (2) At the phase of decreasing asparaginase activity, the Ca2+‐calmodulin‐dependent kinase activity disappeared and a little calmodulin remained associated with the complex: phosphorylation of the complex was increased several‐fold by 1 nMokadaic acid and 25 nMinhibitor‐2, and was not affected by EGTA, indicating a protein phosphatase‐2A‐like activity. (3) When asparaginase activity was low, a little calmodulin was bound to the complex. The kinase could phosphorylate casein and phosvitin. was inhibited by poly(Glu/Tyr 4:1)n. dichloro‐(ribofuranosyl)‐benzimidazole and heparin, stimulated by polylysine and not affected by calmidazolium or EGTA, just as a casein kinase 2. A Ca2+‐dependent but calmodulin‐independent protein phosphatase activity, not affected by okadaic acid and inhibitor‐2. was then identified.We postulate the presence in the complex, of (a) only one protein kinase and one protein phosphatase, whose properties could change during thecycleof asparaginase activity: (b) two Ca2+/‐binding proteins: first calmodulin, which could bind to Ca2+and the casein kinase‐2 form to give a Ca2+/calmodulin‐dependent kinase, which could become Ca2+/calmodulin‐independent following an auto‐phosphorylation process: second a protein homologous to calmodulin, able to bind to the protein phosphatase‐2A catalytic subunit to give