SUMMARY: The activities of L-threonine dehydrogenase (I), 2-amino-3-oxybutyrate: CoA ligase (II), malate synthetase (III), isocitrate lyase (IV), glyoxylate dehydrogenase (V), glycine decarboxylase (VI), L-serine hydroxymethyltransferase (VII), glucan synthetase (VIII), glucose 6-phosphate dehydrogenase (IX) and succinic dehydrogenase (X) were detected in cell-free extracts prepared from the mycelium of the fungus type R. Transfer of to a threonine-containing medium resulted in a significant increase in the intracellular concentrations of L-threonine, glycine, serine and glyoxylate, and a decrease in oxalate. Incubation with C-labelled L-threonine resulted in an immediate output of CO, and an accumulation of labelled glycine and serine in the mycelium. L-Threonine (10 M) increased branching, favoured formation of sclerotia, and induced the formation of enzymes I to VIII, but not IX and X. Sodium oxalate (1.5 x 10 M) inhibited branching, sclerotium formation and the activity of enzymes III and IV. Glycine (10 M) inhibited branching, sclerotium formation and activity of I and II. Ammonium chloride (10 to 10 M) inhibited formation of sclerotia, threonine uptake and activity of III. Acetyl-CoA inhibited V and L-cysteine inhibited I as well as sclerotium formation and branching. It is suggested that hyphal morphogenesis and formation of sclerotia in require an increased supply of carbohydrate intermediates and energy and that these are mainly supplied by the glyoxylate pathway.


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