BIOSYNTHESIS OF AFLATOXIN

强环境致癌物黄曲霉毒素B1的生物合成是 追究 这种霉菌毒素通过以下途径进入食物供应 黄曲霉和A.寄生虫 它们产生这种化合物作为正常代谢物。 慢性摄入 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。 了解其生物合成， 生物有机化学中的基本问题，并可能提供 控制这种环境危害发生的手段。 更新申请中描述的是一套联锁实验 方法来详细定义黄曲霉毒素B1的生物合成。 (1)细胞- 提出了自由实验来研究后双呋喃生物合成 其中versicolorin A的蒽醌核被裂解的步骤， 脱氧、脱羧并重排为 杂色曲霉素 将进行类似的实验来检查 杂色曲霉素进一步转化为黄曲霉毒素。 中间体 将观察到的材料与通过化学合成制备的材料进行比较。 （二） 四氢呋喃氧化去饱和反应的立体化学 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，并测试其 它们对这些酶的不可逆抑制以及它们 在体内起抑制或阻断黄曲霉毒素产生的作用。 （四） 将完成并完全纯化versicolorin B合酶（VBS） 记录，并研究其作用机制。 (5)最近发现的 将进一步研究产生去甲索洛林酸的聚酮合酶（NAS）。 净化和其催化循环检查，特别是关于 通过己酸/己酰辅酶A的表观引发。 (7)编码VBS的基因 和NAS将被克隆和测序，并将与其他 已知的蛋白质序列作为一个更长期的映射目标的前奏 黄曲霉毒素途径结构基因。

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.