Yabe K, Nakamura Y, Nakajima H, Ando Y, Hamasaki T
National Institute of Animal Health, Ibaraki, Japan.
Appl Environ Microbiol. 1991 May;57(5):1340-5. doi: 10.1128/aem.57.5.1340-1345.1991.
5'-Hydroxyaverantin (HAVN) was isolated from a mold, Emericella heterothallica IFO 30842. Aspergillus parasiticus NIAH-26, a UV-irradiated mutant of A. parasiticus SYS-4, produced neither aflatoxins nor precursors in yeast extract-sucrose (YES) medium. When the postmicrosome (cytosol) fraction of NIAH-26, which had been prepared from the culture in YES medium, was incubated with norsolorinic acid (NA) in the presence of NADH or NADPH, averantin (AVN) was produced. The reverse reaction from AVN to NA was promoted by the addition of NAD or NADP (dehydrogenase reaction). When the microsome fraction of NIAH-26 was incubated with AVN, HAVN was produced in the presence of NADPH (monooxygenase reaction). HAVN was, furthermore, oxidized to averufin (AVR) by the cytosol fraction of NIAH-26 in the presence of NAD or NADP (dehydrogenase reaction). In the feeding experiments with A. parasiticus NIAH-26, aflatoxins were produced from AVN, HAVN, NA, and AVR but not from averufanin or averythrin. These results indicate that the reaction sequence NA in equilibrium AVN----HAVN----AVR is involved in the biosynthetic pathway of aflatoxins. The enzyme activities described here were dependent on the culture medium, and no enzyme activities were observed in the nonaflatoxigenic strain A. oryzae SYS-2 (IFO 4251).
5'-羟基杂色曲菌素（HAVN）是从一种霉菌——异宗配合埃默里氏菌IFO 30842中分离得到的。寄生曲霉NIAH-26是寄生曲霉SYS-4的紫外线照射突变体，在酵母提取物-蔗糖（YES）培养基中既不产生黄曲霉毒素，也不产生其前体物质。当从YES培养基培养物中制备的NIAH-26的微粒体后（胞质溶胶）部分在NADH或NADPH存在的情况下与去甲索尔紫红质酸（NA）一起孵育时，会产生杂色曲菌素（AVN）。通过添加NAD或NADP（脱氢酶反应）促进了从AVN到NA的逆反应。当NIAH-26的微粒体部分与AVN一起孵育时，在NADPH存在的情况下会产生HAVN（单加氧酶反应）。此外，在NAD或NADP存在的情况下，NIAH-26的胞质溶胶部分会将HAVN氧化为黄曲霉毒醇（AVR）（脱氢酶反应）。在对寄生曲霉NIAH-26的喂食实验中，黄曲霉毒素是由AVN、HAVN、NA和AVR产生的，但不是由黄曲霉毒醇或红曲菌素产生的。这些结果表明，反应序列NA平衡AVN----HAVN----AVR参与了黄曲霉毒素的生物合成途径。这里描述的酶活性依赖于培养基，在非产黄曲霉毒素菌株米曲霉SYS-2（IFO 4251）中未观察到酶活性。
