| Résumé | Patulin is a potent antibiotic and mycotoxin which is synthesized from acetyl-CoA by Penicillium urticae. In term of intermediates, enzymology, and blocked mutants, the patulin pathway is one of the best characterized pathways of secondary metabolism and nongrowth associated, synchronous appearance of pathway enzymes can be achieved reproducibly. Thus, it is an excellent model for studies with seek to explain the regulation of secondary metabolism. The de novo synthesis of patulin pathway enzymes in initiated by the cessation o replicatory growth at about at 20-21 hours in submerged cultures. The second, fourth, and seventh enzymes of the pathway appeared about 4 hours after the first enzyme, and the later their position in the pathway, the greater was their maximum cellular content. At 15 or 10 C rather than 28 C, the seventh enzyme speared earlier (2 hours) than the second and fourth enzymes. A mutant devoid of the first enzyme produced the second and fourth enzymes at one-tenth their normal levels. Coordinate induction by only a few early pathway metabolites gave normal enzyme levels. The first intrinsic limitation to pathway longevity was the loss of the first enzyme. The earliest pathway enzymes were also the most labile in cell extracts. The most effective increase in longevity (16-32 days) was obtained with carrageenan-immobilized cells. |
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