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.