Regulation von Schlüsselenzymen der Biosynthese aromatischer Aminosäuren in Alkaloid‐bildenden Kulturen von Penicillium cyclopium w.

Abstract In Penicillium cyclopim w., phenylalanin and anthranilate are precursors of the benzodiazepine alkaloids cyclopenin and cyclopenol. The onset and increase of alkaloid biosynthesis in emerged cultures was paralleled by an increase of the in vitro activities of the precursor synthesizing enzymes DAHP synthase 1 ), chorismate mutase, and anthranilate synthase as well as tryptophan synthase. This increase was most pronounced with the DAHP synthase and, therefore, enabled the cells to maintain a constant level of the “central” precursor, chorismate, in the course of alkaloid production. In contrast, the contents of phe, anthranilate as well as tyr and trp decreased with increasing rate of alkaloid synthesis, indicating that the supply of the immediate precursors did not fully compensate the drain towards alkaloid formation. The strongest decrease was seen with the anthranilate content, which was due to several control mechanisms: the increase of anthranilate consuming reactions prior to the anthranilate synthase, the higher capacity of the alternate. phe producing branch of the aromatic pathway, and the feedback inhibition by trp of anthranilate synthase. The formation of anthranilate most probably was the rate limiting step of alkaloid production.