BIOSYNTHESIS OF AFLATOXIN

环境致癌物黄曲霉毒素B1的生物合成 被调查。这种霉菌毒素通过 霉菌黄曲霉和寄生曲霉对粮食的污染 以正常代谢物的形式产生这种化合物。慢性摄取 导致肝脏肿瘤，这是亚洲过早死亡的主要原因， 非洲和中美洲。对其生物合成的理解介绍 生物有机化学中基本感兴趣的问题，并可能提供 控制这种环境危害发生的手段。 介绍了在续订应用中的一套联锁实验 详细定义黄曲霉毒素B1生物合成的方法。(1)单元格- 建议进行自由实验来研究后双呋喃生物合成 花色苷A的蒽醌核被裂解的步骤， 脱氧、脱羧基和重排为 杂色曲霉毒素。将进行类似的实验，以检查 杂色曲霉毒素进一步转化为黄曲霉毒素。中间体 观察到的材料将与通过化学合成制备的材料进行比较。(2) 四氢呋喃氧化脱饱和度的立体化学 将测定二氢双呋喃。(3)基于机理的灭活剂 将合成三种前双呋喃生物合成酶并对其进行检测 它们对这些酶的不可逆转的抑制和它们的能力 在体内起抑制或阻断黄曲霉毒素产生的作用。(4) 杂色苷B合成酶(VBS)的纯化将完成 并对其作用机理进行了研究。(5)最近检测到的 聚酮合成酶(NAS)生产降冰片酸将进一步 提纯并检查其催化循环，特别是关于 由己酸/己酰辅酶A明显引发。(7)VBS基因编码 将对NAS进行克隆和测序，并与其他 已知的蛋白质序列是定位长期目标的前奏 黄曲霉毒素途径的结构基因。

The biosynthesis of the potent environmental carcinogen aflatoxin B1 is to be investigated. This mycotoxin enters the food supply through contamination of grains by the molds Aspergillus flavus and A. parasiticus which produce this compound as a normal metabolite. Chronic ingestion leads to liver tumors that are a major cause of premature death in Asia, Africa and Central America. An understanding of its biosynthesis presents problems of fundamental interest in bioorganic chemistry and may afford means to control the occurrence of this environmental hazard. Described in the renewal application is a set of interlocking experimental approaches to define in detail the biosynthesis of aflatoxin B1. (1) Cell- free experiments are proposed to investigate the post-bisfuran biosynthetic steps in which the anthraquinone nucleus of versicolorin A is cleaved, deoxygenated, decarboxylated and rearranged to the xanthone of sterigmatocystin. Similar experiments will be undertaken to examine the further conversion of sterigmatocystin to aflatoxin. Intermediates observed will be compared to materials prepared by chemical synthesis. (2) The stereochemistry of oxidative desaturation of the tetra- to dihydrobisfuran will be determined. (3) Mechanism-based inactivators of three pre-bisfuran biosynthetic enzymes will be synthesized and tested for their irreversible inhibition of these enzymes and their ability to function in vivo to inhibit or block aflatoxin production. (4) Purification of versicolorin B synthase (VBS) will be completed and fully documented, and its mechanism of action studied. (5) A recently detected polyketide synthase (NAS) producing norsolorinc acid will be further purified and its catalytic cycle examined, particularly with regard to apparent initiation by hexanoate/hexanoylCoA. (7) The genes coding for VBS and NAS will be cloned and sequenced, and comparisons will be made to other known protein sequences as a prelude to a longer term objective of mapping the aflatoxin pathway structural genes.