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首页> 外文期刊>Biochemistry >Effect of transition-state analogues on the redox properties of medium-chain acyl-CoA dehydrogenase.
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Effect of transition-state analogues on the redox properties of medium-chain acyl-CoA dehydrogenase.

机译：过渡态类似物对中链酰基辅酶A脱氢酶氧化还原特性的影响。

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摘要

The binding of substrate/product or transition-state intermediates modifies the properties of medium-chain fatty acyl-CoA dehydrogenase (MCAD) by causing the redox potential to shift positive and the oxygen reactivity to slow by 3000-fold. Two ligands, identified as being the most effective in slowing oxygen reactivity, were 2-azaoctanoyl-CoA and 3-thiaoctanoyl-CoA [Wang, R., & Thorpe, C. (1991) Biochemistry 30, 7895-7901]. We have measured the potential shifts caused by the binding of both ligands to determine which is most similar to the potential shift caused by substrate/product mixture, the assumption being that the best transition-state structural intermediate would give the potential shift most similar to that of substrate/product [Lenn, N.D., Stankovich, M.T., & Liu, H. (1990) Biochemistry 29, 10594-10602]. Both ligands shifted the potential positive, but the shift caused by 2-azaoctanoyl-CoA was 65% that of substrate/product, while 3-thiaoctanoyl-CoA was only 20% of that value. This positive shift is proposed to be caused by a resonance form stabilized by the interaction of the catalytically essential carbonyl of the acyl-CoA with two hydrogen bonds from the enzyme, which induces a partial negative charge on the carbonyl and a partial positive charge on carbon 2 of the ligand and carbon 3 of the substrate/product couple. The X-ray structure shows that carbons 2 and 3 of the substrate/product overlap the diazadiene portion of the flavin ring [Kim, J.-J. P., Wang, M., & Paschke, R. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 7523-7527].(ABSTRACT TRUNCATED AT 250 WORDS)
机译：底物/产物或过渡态中间体的结合通过引起氧化还原电位正向移动和氧反应性降低3000倍来修饰中链脂肪酰基辅酶A脱氢酶（MCAD）的特性。被鉴定为最有效的减缓氧反应性的两个配体是2-氮杂辛酰基-CoA和3-硫杂辛酰基-CoA [Wang，R。和Thorpe，C。（1991）Biochemistry 30，7895-7901]。我们已经测量了由两个配体的结合引起的电势漂移，以确定哪个最类似于由底物/产物混合物引起的电势漂移，这是假设最佳的过渡态结构中间体会给出的电势漂移最相似。底物/产物的制备[Lenn，ND，Stankovich，MT，和Liu，H。（1990）Biochemistry 29，10594-10602]。两个配体均使电位正向移位，但是由2-氮杂辛酰基-CoA引起的移位为底物/产物的65％，而由3-硫杂辛酰基-CoA引起的移位仅为该值的20％。提出这种正位移是由共振形式引起的，该共振形式通过酰基辅酶A的催化必不可少的羰基与酶的两个氢键相互作用而稳定，从而在羰基上诱导部分负电荷，在碳上诱导部分正电荷配体的碳原子数为2，底物/产物的碳原子数为3。 X射线结构显示底物/产物的碳2和3与黄素环的二氮杂二烯部分重叠[Kim，J. P.，Wang，M.和Paschke，R.（1993年），美国国家科学院院刊。 Natl。学院科学[U.S.A. 90，7523-7527]。（摘要以250字截断）

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