Parry R J, Li W
Department of Chemistry, Rice University, Houston, Texas 77005-1892, USA.
Arch Biochem Biophys. 1997 Mar 1;339(1):47-54. doi: 10.1006/abbi.1996.9857.
Streptomyces viridifaciens MG456-hF10 produces the antitumor agent valanimycin, which is a member of a family of antibiotics containing the azoxy group. An enzyme involved in the biosynthesis of valanimycin has been purified 360-fold from S. viridifaciens. This enzyme, isobutylamine N-hydroxylase, catalyzes the oxidation of isobutylamine to isobutylhydroxylamine in the presence of oxygen and a reduced flavin cofactor. Unlike other known N-hydroxylases, isobutylamine N-hydroxylase cannot carry out the reduction of the flavin cofactor. Rather, the reduced flavin is supplied by a separate flavin reductase that is present in extracts of S. viridifaciens. The reduced flavin cofactor could also be supplied by the flavin mononucleotide reductase of Vibrio fischeri. The requirement for molecular oxygen and a reduced flavin indicates that the N-hydroxylase is a flavin monooxygenase and that the mechanism for the hydroxylation is likely to proceed via the formation of a flavin 4a-hydroperoxide. Isobutylamine N-hydroxylase exhibited a subunit molecular mass of 40 kDa and existed in dimeric or trimeric form depending upon buffer conditions. The pI of the protein was found to be ca. 5.1 and the enzyme exhibited a sensitivity to thiol-directed reagents.
绿色产色链霉菌MG456-hF10可产生抗肿瘤药物瓦拉霉素，它是一类含有偶氮氧基的抗生素家族的成员。一种参与瓦拉霉素生物合成的酶已从绿色产色链霉菌中纯化出来，纯化倍数为360倍。这种酶，异丁胺N-羟化酶，在氧气和还原型黄素辅因子存在的情况下，催化异丁胺氧化为异丁羟胺。与其他已知的N-羟化酶不同，异丁胺N-羟化酶不能进行黄素辅因子的还原。相反，还原型黄素由绿色产色链霉菌提取物中存在的一种单独的黄素还原酶提供。还原型黄素辅因子也可以由费氏弧菌的黄素单核苷酸还原酶提供。对分子氧和还原型黄素的需求表明，N-羟化酶是一种黄素单加氧酶，并且羟基化机制可能通过黄素4a-氢过氧化物的形成来进行。异丁胺N-羟化酶的亚基分子量为40 kDa，并根据缓冲条件以二聚体或三聚体形式存在。发现该蛋白质的pI约为5.1，并且该酶对硫醇导向试剂敏感。
