Schliemann W, Kobayashi N, Strack D
Abteilung Sekundarstoffwechsel, Institut fur Pflanzenbiochemie, Halle (Saale), Germany.
Plant Physiol. 1999 Apr;119(4):1217-32. doi: 10.1104/pp.119.4.1217.
Experiments were performed to confirm that the aldimine bond formation is a spontaneous reaction, because attempts to find an enzyme catalyzing the last decisive step in betaxanthin biosynthesis, the aldimine formation, failed. Feeding different amino acids to betalain-forming hairy root cultures of yellow beet (Beta vulgaris L. subsp. vulgaris "Golden Beet") showed that all amino acids (S- and R-forms) led to the corresponding betaxanthins. We observed neither an amino acid specificity nor a stereoselectivity in this process. In addition, increasing the endogenous phenylalanine (Phe) level by feeding the Phe ammonia-lyase inhibitor 2-aminoindan 2-phosphonic acid yielded the Phe-derived betaxanthin. Feeding amino acids or 2-aminoindan 2-phosphonic acid to hypocotyls of fodder beet (B. vulgaris L. subsp. vulgaris "Altamo") plants led to the same results. Furthermore, feeding cyclo-3-(3,4-dihydroxyphenyl)-alanine (cyclo-Dopa) to these hypocotyls resulted in betanidin formation, indicating that the decisive step in betacyanin formation proceeds spontaneously. Finally, feeding betalamic acid to broad bean (Vicia faba L.) seedlings, which are known to accumulate high levels of Dopa but do not synthesize betaxanthins, resulted in the formation of dopaxanthin. These results indicate that the condensation of betalamic acid with amino acids (possibly including cyclo-Dopa or amines) in planta is a spontaneous, not an enzyme-catalyzed reaction.
进行了实验以证实醛亚胺键的形成是一个自发反应，因为试图找到一种催化甜菜色素生物合成中最后决定性步骤（醛亚胺形成）的酶的尝试失败了。给黄色甜菜（Beta vulgaris L. subsp. vulgaris “Golden Beet”）形成甜菜红素的毛状根培养物投喂不同的氨基酸，结果表明所有氨基酸（S型和R型）都能产生相应的甜菜黄素。在此过程中，我们既未观察到氨基酸特异性，也未观察到立体选择性。此外，通过投喂苯丙氨酸解氨酶抑制剂2-氨基茚-2-膦酸来提高内源性苯丙氨酸（Phe）水平，产生了源自Phe的甜菜黄素。给饲料甜菜（B. vulgaris L. subsp. vulgaris “Altamo”）植株的下胚轴投喂氨基酸或2-氨基茚-2-膦酸也得到了相同的结果。此外，给这些下胚轴投喂环-3-(3,4-二羟基苯基)-丙氨酸（环多巴）会导致甜菜红苷的形成，这表明花青素形成中的决定性步骤是自发进行的。最后，给已知积累高水平多巴但不合成甜菜黄素的蚕豆（Vicia faba L.）幼苗投喂甜菜醛氨酸，导致了多巴黄素的形成。这些结果表明，在植物中甜菜醛氨酸与氨基酸（可能包括环多巴或胺）的缩合是一个自发反应，而非酶催化反应。
