Effects of 8-azaguanine, chloramphenicol and 3-amino-1,2,4-triazole on riboflavin formation by Eremothecium ashbyii.

Abstract

The central problem inquired in this investigation is an attempt to elucidate how synthesis of the consecutive enzymes comprising the biosynthetic pathway directing to riboflavin is correlated with the life cycle of a flavinogenic fungus, Eremothecium ashbyii. The inhibition tests with three types of well known inhibitors to affect the fungal growth and riboflavinogenesis are employed for this purpose. The evidences presented as enumerated in the followings offers a powerful support for a suggestion that synthesis of the flavinogenic enzymes might be strictly controlled to progress within a confined period in the life cycle, which locates in an earlier stage of the fungal rapid growing phase. The life cycle can be roughly divided by three phases of the fungal growth, growth cessation and autolysis. The most striking attribute is an evidence that riboflavinogenesis can not be coupled with the growth: accumulation of the vitamin initiates just in coincidence with the growth cessation, and continues uninterrupted even at onset of the autolysis.1. Riboflavin production is inhibited abruptly by 8-azaguanine within the narrow range of its low concentration. The flavinogenic inhibition can be paralleled with the growth injury of the fungi. The mycelial colonies under this situation are abnormal to develop just like lumps with hard paddings. Such a tendency is more remarkable in an agar slant culture containing the poison. This phenomenon is not a mutation, since transplantation of this fungi into a fresh slant devoid of the inhibitor can reverse both the growth and flavinogenic capacities identical with the normal strain. Effects of 8-azaguanine are tightly linked with the fungal life cycle. The agent is most effective as a potent inhibitor for riboflavinogenesis, when exists in an earlier stage of the growth phase. Addition of the drug after this stage causes only a slight effect on the vitamin formation. In order to explain these findings, a model is more reasonable to be proposed based on the accepted connotation, that synthesis of the enzymes organizing riboflavinogenic pathway is prevented by incorporating the abnormal base into the corresponding metabolic unstable ribonucleic acid strands such as messenger or transfer ribonucleic acids. This implies that the information from deoxyribonucleic acid molecules to the specific enzymes can be disturbed by the incorporation. The present evidences reveal that these genic processes of transcription and translation can proceed during the earlier period of the growth phase.2. The model suggested by the previous experiments is ascertained by using an inhibitor specific to protein synthesis, chloramphenicol. A reciplocity is present between both inhibitions caused by the antibiotic of the growth and riboflavinogenesis. The inhibition of the vitamin production is intimately associated with the life cycle of the fungus. Induction of a strong blockage requires an essential existence of the inhibitor in the earlier stage of the growth phase. These two evidences can provide a rational suggestion that the enzymes implicated in riboflavinogenesis are synthesized during this period. This idea does not conflict with the data from 8-azaguanine functions.3. 3-Amino-1, 2, 4-triazole prevents riboflavin yield without influencing the growth. The inhibitory power of the agent fails to be connected with the life cycle of the fungus, into some phases of which supplement with the antagonist raises a prompt inhibition of the vitamin production without a lag. These facts indicates that the triazole is restricted in its action: it can operate immediately on the intermediary step (s), but not on the synthesis of the enzymes, constructing riboflavinogenic pathway.