Huizinga E G, van Zanten B A, Duine J A, Jongejan J A, Huitema F, Wilson K S, Hol W G
Department of Chemistry, Groningen University, The Netherlands.
Biochemistry. 1992 Oct 13;31(40):9789-95. doi: 10.1021/bi00155a036.
To identify the reactive part of the orthoquinone function of the tryptophan-derived cofactor found in methylamine dehydrogenase (MADH), we have determined the crystal structures of MADH from Thiobacillus versutus inhibited by methylhydrazine and (2,2,2-trifluoroethyl)hydrazine. Extra electron density attached to C6 of the tryptophyl tryptophanquinone cofactor shows that this atom and not C7 is the reactive part of the ortho-quinone moiety. The density retained after hydrazine inhibition is much less extensive than expected, however, suggesting that partial breakdown of the inhibitors after reaction with the cofactor may take place. A detailed description is presented of the cofactor environment in an improved model of MADH which now includes information from the recently determined gene sequence of the cofactor-containing subunit [Ubbink, M., van Kleef, M.A.G., Kleinjan, D., Hoitink, C.W.G., Huitema, F., Beintema, J.J., Duine, J.A., & Canters, G.W. (1991) Eur. J. Biochem. 202, 1003-1012]. We hypothesize that Asp76 is responsible for proton abstraction from the alpha-carbon of the substrate during catalysis.
为了确定在甲胺脱氢酶（MADH）中发现的色氨酸衍生辅因子邻醌功能的反应部分，我们测定了受甲基肼和（2,2,2-三氟乙基）肼抑制的来自硫杆菌的MADH的晶体结构。附着在色氨酸-色氨酸醌辅因子C6上的额外电子密度表明，该原子而非C7是邻醌部分的反应部分。然而，肼抑制后保留的密度比预期的要小得多，这表明抑制剂与辅因子反应后可能会发生部分分解。本文详细描述了MADH改进模型中的辅因子环境，该模型现在包含了来自最近确定的含辅因子亚基基因序列的信息[Ubbink, M., van Kleef, M.A.G., Kleinjan, D., Hoitink, C.W.G., Huitema, F., Beintema, J.J., Duine, J.A., & Canters, G.W. (1991) Eur. J. Biochem. 202, 1003 - 1012]。我们推测Asp76在催化过程中负责从底物的α-碳上夺取质子。
