Casella L, Poli S, Gullotti M, Selvaggini C, Beringhelli T, Marchesini A
Dipartimento di Chimica Generale, Università di Pavia, Italy.
Biochemistry. 1994 May 31;33(21):6377-86. doi: 10.1021/bi00187a001.
The reactivity of a series of para-substituted phenolic compounds in the peroxidation catalyzed by chloroperoxidase was investigated, and the results were interpreted on the basis of the binding characteristics of the substrates to the active site of the enzyme. Marked selectivity effects are observed. These operate through charge, preventing phenolic compounds carrying amino groups on the substituent chain to act as substrates for the enzyme, and through size, excluding potential substrates containing bulky substituents to the phenol nucleus. Also, chiral recognition is exhibited by chloroperoxidase in the oxidation of N-acetyltyrosine, where only the L isomer is oxidized. Kinetic measurements show that, in general, the efficiency of chloroperoxidase in the oxidation of phenols is lower than that of horseradish peroxidase. Paramagnetic NMR spectra and relaxation rate measurements of chloroperoxidase-phenol complexes are consistent with binding of the substrates close to the heme, in the distal pocket, with the phenol group pointing toward the iron atom. On the other hand, phenolic compounds which are not substrates for chloroperoxidase bind to the enzyme with a much different disposition, with the phenol group very distant from the iron and probably actually outside the active-site cavity.
研究了一系列对取代酚类化合物在氯过氧化物酶催化的过氧化反应中的反应活性，并根据底物与酶活性位点的结合特性对结果进行了解释。观察到明显的选择性效应。这些效应通过电荷起作用，阻止在取代基链上带有氨基的酚类化合物作为酶的底物，还通过尺寸起作用，排除酚核含有庞大取代基的潜在底物。此外，氯过氧化物酶在N - 乙酰酪氨酸的氧化中表现出手性识别，其中只有L - 异构体被氧化。动力学测量表明，一般来说，氯过氧化物酶氧化酚类的效率低于辣根过氧化物酶。氯过氧化物酶 - 酚复合物的顺磁核磁共振光谱和弛豫速率测量结果与底物在远端口袋中靠近血红素的结合一致，酚基团指向铁原子。另一方面，不是氯过氧化物酶底物的酚类化合物以非常不同的取向与酶结合，酚基团离铁很远，可能实际上在活性位点腔之外。
