[Effect of iron, actinomycin D and cycloheximide on the GTP-cyclohydrolase synthesis in flavinogenic yeasts]

The effect of Fe on the GTP-cyclohydrolase activity of the yeasts Pichia guilliermondii ATCC 9058 and Torulopsis candida BKM 13 whose flavinogenesis is controlled by Fe was investigated. The GTP-cyclohydrolase activity of yeast cells grown in an iron-deficient medium was 40-50 times that of the cells grown in an iron-rich medium. In the latter case the incubation of cells with alpha, alpha'-dipyridyl or 8-oxyquinoline also increased the enzyme activity. Cycloheximide prevented the rise in the cyclohydrolase activity in both cases, thus suggesting the participation of Fe in the control of the enzyme synthesis. Actinomycin D inhibited the enzyme derepression induced by alpha, alpha1-dipyridyl or 8-oxyquinoline in the P. guilliermondii MS1-37 mutant possessing a high sensitivity to this antibiotic. It is assumed that Fe is involved in the control of GTP-cyclohydrolase synthesis in flavinogenic yeasts at the transcription level.