Wickwire B M, Harris C M, Harris T M, Broquist H P
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
J Biol Chem. 1990 Sep 5;265(25):14742-7.
The biosynthesis of pipecolic acid from L-lysine in the fungal parasite, Rhizoctonia leguminicola has been reinvestigated. Pipecolate is then utilized to form the toxic octahydroindolizine alkaloids, slaframine and swainsonine. Incorporation studies of L-versus D-[U-14C]lysine into R. leguminicola metabolites confirmed earlier findings that L-lysine is the predominant substrate for pipecolate formation and D-lysine for alpha-N-acetyllysine (concerned in lysine catabolism). However [alpha-15N]lysine, not [epsilon-15N]lysine as previously reported, labeled pipecolate. Such findings implied that delta 1-piperideine-6-carboxylate, not delta 1-piperideine-2-carboxylate, was formed from lysine and was the immediate precursor of pipecolate. Evidence from cell-free enzyme systems established the following biosynthetic events: L-lysine A----saccharopine B----delta 1-piperideine-6-carboxylate C----pipecolate. Products of reactions A and C were identified from biological and chemical considerations. Reaction B was carried out by a previously undescribed flavin enzyme termed saccharopine oxidase. The product of reaction B, which reacted with p-dimethylaminobenzaldehyde, was reduced with Na-CNB2H3. Its NMR spectrum was identical with that of deuteriated pipecolate prepared from authentic delta 1-piperideine-6-carboxylate, but not from authentic delta 1-piperideine-2-carboxylate. Reaction B represents a branching of primary lysine metabolism from saccharopine to a secondary pathway leading to pipecolate and to octahydroindolizine alkaloids in R. leguminicola.
对真菌寄生菌豆科丝核菌中由L-赖氨酸生物合成哌啶酸的过程进行了重新研究。然后，哌啶酸被用于形成有毒的八氢吲哚嗪生物碱——苜蓿胺和苦马豆素。用L-与D-[U-¹⁴C]赖氨酸对豆科丝核菌代谢物的掺入研究证实了早期的发现，即L-赖氨酸是哌啶酸形成的主要底物，而D-赖氨酸是α-N-乙酰赖氨酸（参与赖氨酸分解代谢）的底物。然而，标记哌啶酸的是[α-¹⁵N]赖氨酸，而非先前报道的[ε-¹⁵N]赖氨酸。这些发现表明，哌啶酸是由赖氨酸形成的δ¹-哌啶-6-羧酸而非δ¹-哌啶-2-羧酸，并且是哌啶酸的直接前体。无细胞酶系统的证据确定了以下生物合成过程：L-赖氨酸A→酵母氨酸B→δ¹-哌啶-6-羧酸C→哌啶酸。从生物学和化学方面考虑确定了反应A和C的产物。反应B由一种先前未描述的黄素酶——酵母氨酸氧化酶催化进行。反应B的产物与对二甲基氨基苯甲醛反应，用Na-CNB₂H₃还原。其核磁共振谱与由 authentic δ¹-哌啶-6-羧酸而非 authentic δ¹-哌啶-2-羧酸制备的氘代哌啶酸的谱图相同。反应B代表了豆科丝核菌中赖氨酸初级代谢从酵母氨酸分支到导致哌啶酸和八氢吲哚嗪生物碱的次级途径。
