30 酵素レベルに於ける菌類代謝産物の生合成研究 : Seco-anthraquinone,(+)Geodin生合成に関与する酵素系について

抄録

(+)Geodin (1), a seco-anthraquinone, is an antibiotic produced by fungi. Its biosynthesis has been studied by extensive feeding experiments and established as shown in Fig. 1. A variety of reactions involved in the biosynthsis of (+)geodin (1) drew our attention and we have studied the purification and characterization of the enzymes for (+)geodin (1) biosynthesis in Aspergillus terreus IMI 16043. i) Emodinanthrone oxygenase was detected in cell free system and analyses of the enzymically formed emodin (3) by MS and ^<13>C-NMR confirmed the incorporation of molecular oxygen into corresponding site of emodin (3). ii) Emodin O-methyltransferase, an enzyme catalyzing methylation of emodin (3) to produce questin (4), was purified up to 89 fold by Blue Sepharose and Sepharose 6B. This enzyme was found to have low Km value and high specificity for emodin (3). iii) Questin oxygenase system, which converts questin (4) into benzophenone, desmethylsulochrin (5) by a Baeyer-Villiger type oxidation, was observed in soluble fraction, and fractionated into two activities, an unstable oxygenase and possibly an NADPH oxidase. iv) Final step of (+)geodin (1) biosynthesis is phenol oxidative coupling reaction catalyzed by Dihydrogeodin oxidase. The purified oxidase exhibited characteristics of blue copper protein and the presence of copper was confirmed by atomic absorption analysis. Dihydrogeodin oxidase is the first phenol oxidative coupling enzyme specific for natural product biosynthesis which has been purified and characterized.