Abstract
Alkaloids cannot be supposed to be waste products of general metabolism. They are formed only for a relatively brief time during the lifespan of the culture and under conditions of reduced proliferation. Living rather than dying cells are required for alkaloid synthesis. The alkaloid yield and differentiated cells were observed to be inversely proportional. This pattern is correlated with formation of secondary shunt products. The district between the cell-pool tryptophan “down” and “up” phases is a promising target for the investigation of regulation of the alkaloid formation and continuous fermentation of these compounds. Considering the general phenomenon of secondary metabolism we may guess that alkaloid formation includes derepression of the appropriate portion of the genome to obtain transcription and translation of specific synthetases and subsequent activity of these enzymes for a relatively brief period. The ability to produce alkaloids is not only easily lost genetically, but is also extraordinarily susceptible to suppression by rather minor environmental manipulations. The production of alkaloids occurs only in nutrient media with high osmotic pressure. Ergoline alkaloids do not definitely belong to a group of physiologically inert secondary metabolites. They are, in fact, able to influence primary shunt metabolism, and may reflect a regulatory device of the producing cell. Alkaloids increase the activities of tryptophan synthetase and acetyl-CoA carboxylase of the ergot fungus and exert a negative effect on citrate synthase, isocitrate lynse, and malate synthase. Also inhibition of Claviceps peptidases by peptide alkaloids is of peculiar interest. Addition of ergometrine (10 -4 M) to the submerged culture of C. paspali increased the total-alkaloid yield by 120%. However, the stimulatory effect was inversely proportional to the concentration of the supplied ergometrine. Implicit in these data is that in alkaloid-producing cultures accumulating alkaloids may suppress the attainment of the yield that would be achieved by continuous control of the alkaloid level. Man weiß seit langem, daß im allgemeinen Mutterkornzuchtstämme, die unter parasitischen Bedingungen reichlich Alkaloide bilden, bei der saprophytischen Kultivation keine oder nur in Spuren Ergoline synthetisieren. Die vorliegende Übersicht ist ein Beitrag zur Problematik der Physiologie der Alkaloidbildung bei saprophytischen Claviceps -Arten. Die Mutterkornalkaloide treten nur in bestimmten Entwicklungsstadien der Kultur und unter Bedingungen der reduzierten Proliferation auf. Meistens ist die Alkaloidsynthese mit herabgesetzter Zelldifferenzierung verknüpft. Die Fähigkeit des Stammes, Alkaloide zu bilden, ist stark abhängig vom eingesetzten Medium. Die Schlüsselsubstanz aller Ergoline ist das Tryptophan. Der Abschnitt zwischen der Phase des Absinkens und der Phase des Anstiegs des freien Zelltryptophans ist anscheinend ein vielversprechender Ansatzpunkt für die Steuerung der Alkaloidsynthese und für die kontinuierliche Fermentation der Alkaloide. Die Mutterkornalkaloide beeinflussen einige wichtige Enzyme des primären Stoffwechscls, z. B. stimulieren sie die Tryptophansynthetase und die Acetyl-CoA-Karboxylase und hemmen die Citratsynthetase, Isocitratlyase, Malatsynthetase und die intracellulären Exopeptidasen der Claviceps -Stämme. Nach dem Einsatz von Ergometrin (10 -4 M) in die Claviceps -Tiefkultur steigt die Alkaloidausbeute um 120%. Der Effekt hängt von der Menge des zugegebenen Ergometrins ab. Man kann annehmen, daß die Mutterkornalkaloide physiologisch aktive Metabolite darstellen und sich an der Regulation ihrer eigenen Synthese beteiligen.
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More From: Zentralblatt fuer Bakteriologie, Parasitenkunde, Infektionskrankheiten und Hygiene. Zweite Naturwissenschaftliche Abteilung: Allgemeine, Landwirtschaftliche und Technische Mikrobiologie
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