Thermolysis of the CoC bond in adenosylcobalamin (coenzyme B12)—IV. Products, kinetics and CoC bond dissociation energy studies in ethylene glycol
作者:Benjamin P. Hay、Richard G. Finke
DOI:10.1016/s0277-5387(00)81775-1
日期:1988.1
trap TEMPO proceeds with four isosbestic points to yield 100±2% Co(II)B 12 and two nucleoside products, 8,5′-anhydroadenosine and 5′-deoxyadenosine. In the presence of >10 −2 M TEMPO, the TEMPO-trapped Ado . product (T-Ado) and Co(II)B 12 account quantitatively for the starting AdoB 12 . From HPLC studies of the concentration of the nucleoside products vs [TEMPO], absolute rate constants at 110°C for
摘要在引言概述了腺苷钴胺素(AdoB 12)键均解问题的关键问题之后,介绍了AdoB 12在乙二醇中热解的产物,动力学和CoC5'键解离能的详细信息。在不存在氮氧自由基捕获器TEMPO的情况下,AdoB 12的厌氧热解进行四个同构异构点,得到100±2%Co(II)B 12和两个核苷产物,8,5'-脱水腺苷和5'-脱氧腺苷。在> 10 -2 M TEMPO的情况下,TEMPO陷获的Ado。产物(T-Ado)和Co(II)B 12在数量上占起始AdoB 12的比例。通过HPLC研究核苷产物的浓度与[TEMPO]的关系,得出Ado在110°C时的绝对速率常数。环化及其H。首次从乙二醇溶剂中提取 kc(110℃)≤5×10 5 s -1和ka(110℃)≤7×10 3 M -1 s -1。在添加真实的Co(II)B 12的情况下进行的动力学研究表明,1 / [Kobs与[Co(II)B 12]
Gani, David; Hollaway, Michael R.; Johnson, Alan W., Journal of Chemical Research, Miniprint, 1981, # 7, p. 2327 - 2344
作者:Gani, David、Hollaway, Michael R.、Johnson, Alan W.、Lappert, Michael F.、Wallis, O. Caryl
DOI:——
日期:——
Thermolysis of the cobalt-carbon bond of adenosylcobalamin. 2. Products, kinetics, and cobalt-carbon bond dissociation energy in aqueous solution
作者:Benjamin P. Hay、Richard G. Finke
DOI:10.1021/ja00276a020
日期:1986.8
Synthesis and Characterization of 3‘,4‘-Anhydroadenosylcobalamin: A Coenzyme B<sub>12</sub> Analogue with Unusual Properties
作者:Olafur Th. Magnusson、Perry A. Frey
DOI:10.1021/ja0013780
日期:2000.9.1
The question of how coenzyme B-12-dependent enzymes facilitate the cleavage of the Co-C bond of the cofactor is of interest. We have synthesized an analogue of 5'-deoxyadenosylcobalamin (AdoCbl(1)) designed to stabilize the 5'-deoxyadenosyl radical (5'-deoxyadenosine-5'-yl) that is produced upon homolysis of the Co-C bond. By replacement of the upper axial ligand of AdoCbl by a 3',4'-anhydro-5'-deoxyadenosyl moiety, the radical formed on the nucleoside analogue is stabilized by allylic delocalization. The compound, 5'-deoxy- 3',4'-anhydroadenosylcobalamin (3',4'-anAdoCbl) was synthesized by chemical and enzymatic methods. The final step was coupling of cob(I)alamin and 3',4'-anhydroATP catalyzed by CobA, an ATP: corrinoid adenosyltransferase. 3',4'-anAdoCbl displays interesting properties. The compound has not been purified to homogeneity due to its thermal and oxygen sensitivity. It was characterized by UV-vis spectroscopy, ESI-MS, and NMR spectroscopy. The bond dissociation energy of the Co-C bond of the analogue was measured by radical trapping techniques. A significantly weaker bond (24 +/- 2 kcal/mol) as compared to AdoCbl (30 kcal/mol) was observed, as was homolytic cleavage at ambient temperature. Photolysis experiments conducted under anaereobic conditions reveal no formation of cob(II)alamin, whereas the compound breaks down rapidly under aerobic conditions as measured by cob(In)alamin formation. We postulate that the weak Co-C bond is cleaved reversibly by photolysis, where recombination of the allylic radical and cob(II)alamin occurs efficiently in the absence of a radical scavanger. Activation of the coenzyme Bit-dependent enzymes diol dehydrase and ethanolamine ammonia-lyase was observed with the cofactor analogue. The measured activity was low and no formation of cob(II)alamin could be detected in the steady-state of the reaction for either enzyme. Comparative interactions of AdoCbl and 3',4'-anAdoCbl with diol dehydrase and ethanolamine ammonia-lyase suggest that cleavage of the Co-C bond is facilitated by enzyme-coenzyme binding contacts that are remote from the Co-C bond.
Synthese de la cyclo-5'-8 desoxy-5' adenosine: stereochimie et mecanisme de la cyclisation d'un derive de l'iodo-5' adenosine par le zinc