Mechanism of .alpha.-ketoglutarate oxidation in coupled enzymic oxygenations
Mechanism of .alpha.-ketoglutarate oxidation in coupled enzymic oxygenations
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偶联酶氧化中α-酮戊二酸氧化的机制
DOI：
10.1021/ja01044a082
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发表时间：
1969
影响因子：
15
通讯作者：
S. Lindstedt
中科院分区：
文献类型：
--
作者：
B. Lindblad;G. Lindstedt;M. Tofft;S. Lindstedt
(14)对于两种二核苷酸的无序过程，获得了相同的值（Δ H = 8.1 kcal/mol），而AmpAm的AS 0（28 eu/mol）略高于阿帕的AS 0（27 eu/mol）。相应地，AmpAm（0.3千卡/摩尔）的Δ Fat 0低于阿帕（0.6千卡/摩尔）。较大的AS值和AmpAm有序结构的较低稳定性可能是由于AmpAm在无序化过程中获得的转动自由度大于阿帕。Corey-Pauling-Koltum模型的建立表明，在AmpAm的有序构象中，大体积甲基取代基的引入会降低主链的柔性。极性羟基被基本上非极性的甲氧基取代而引起的溶剂化作用的变化也可能是重要的。虽然这种解释似乎是合理的，但应记住以下几点：为了确定Tm和推导热力学数据，必须近似解链曲线的高温和低温分支。这可能会引起相当大的误差，特别是对于曲线的低温端。此外，热力学处理是基于两态模型，这是不明确的建立。
(14) Identical values are obtained for the enthalpies of the disordering process for both dinucleotides (AH= 8.1 kcal/mol), while AS0 is slightly higher for AmpAm (28 eu/mol) than for ApA (27 eu/mol). Correspondingly, AFat 0 is lower for AmpAm (0.3 kcal/mole) than for ApA (0.6 kcal/mole). The larger value for AS and the lower stability of the ordered structure of AmpAm may be due to a larger amount of rotational freedom gained in the disordering process of AmpAm than of ApA. Model building (Corey-Pauling-Koltum mod-els) indicates thatintroduction of the bulky methyl substituentsmay diminish the flexibility of the backbone predominantly in the ordered con-formation of AmpAm. A change in solvation resulting from thereplace-ment of the polar hydroxyls by essentially nonpolar methoxy groupsmay also be of importance. While this interpretation seems plausible, the following shouldbe kept in mind: for the determination of the Tm’s and the derivation of the thermodynamic data the high-and the low-temperature branches of the melting curves have to be approximated. This may give rise to considerable error, especially for the low-temperature ends of the curves. Furthermore, the thermodynamic treat-ment is based on the two-state model which is not clearly established.