Glutamate decarboxylase activity in Trichoderma viride conidia and developing mycelia

Glutamic acid decarboxylase (GAD) activity was measured in homogenates of c onidia and both submerged and aerial mycelia of Trichoderma viride. The GAD activity in conidia had a temperature optimum at 30 degreesC and a pH opti mum at pH 4. GAD was stimulated by EDTA (2 mM) and was insensitive to treat ment with calmodulin antagonists calmidazolium (10 muM) or phenothiazine ne uroleptics (60 muM) Cyclosporin A (up to 300 muM) partially inhibited GAD i n the homogenate, but not in the supernatant obtained after centrifuging th e homogenate. Attempts to release GAD activity from the homogenate using hi gh ionic strength, detergents, or urea failed. Freezing-thawing led to the partial increase of activity in the conidial homogenate. These results indi cate that GAD is a membrane-bound enzyme. The highest specific activity of GAD was present in the mitochondrial/vacuolar organellar fraction. Germinat ion of conidia in the submerged culture led to a temporary decrease in GAD activity. After prolonged cultivation, the activity displayed quasi-oscilla tory changes. The stationary state was characterized by a high GAD activity . The presence of gamma -aminobutyric acid in the submerged mycelia was dem onstrated. In surface culture in the dark, GAD activity increased in a mono phasic manner until conidia formation. The illumination of dark-cultivated mycelia by a white-light pulse caused a dramatic increase in GAD activity. Light-induced changes were not observed in mutants with delayed onset of co nidiation. In the dark or upon illumination by light pulse, the increase of GAD activity preceded the appearance of conidia. Thus, GAD activity in T. viride is closely associated with its developmental status and may represen t a link between differentiation events and energy metabolism.