Lee H C, Cummings K, Hall K, Hager L P, Oldfield E
School of Chemical Sciences, University of Illinois, Urbana-Champaign 61801.
J Biol Chem. 1988 Nov 5;263(31):16118-24.
We have obtained oxygen-17 (17O) nuclear magnetic resonance (NMR) spectra of C17O ligands bound to ferrous horseradish peroxidase isozyme A, isozyme C, and ferrous chloroperoxidase, as a function of pH. Our results show that the peroxidases exist in two distinct states, the acidic and alkaline forms, which undergo reversible acid-base-induced transitions characterized by a single pK value. The two forms are characterized spectroscopically in much the same way in all three proteins, suggesting a similar structural origin for the transition process. In particular, the 17O NMR signal of the acidic form is approximately 7 ppm more shielded than that of the alkaline form, and the CO ligand in the acidic form appears to have a smaller 17O nuclear quadrupole coupling constant than that of the alkaline form. We have also obtained the pK values and exchange rates for all three peroxidases. The results indicate that a similar structural change may be involved in the transition process in all three peroxidases.
我们已获取了与亚铁辣根过氧化物酶同工酶A、同工酶C以及亚铁氯过氧化物酶结合的C17O配体的氧-17（17O）核磁共振（NMR）谱，该谱是pH的函数。我们的结果表明，过氧化物酶以两种不同状态存在，即酸性形式和碱性形式，它们经历以单个pK值为特征的可逆酸碱诱导转变。在所有三种蛋白质中，这两种形式在光谱上的特征大致相同，这表明转变过程具有相似的结构起源。特别是，酸性形式的17O NMR信号比碱性形式的屏蔽约7 ppm，并且酸性形式中的CO配体似乎比碱性形式具有更小的17O核四极耦合常数。我们还获得了所有三种过氧化物酶的pK值和交换速率。结果表明，所有三种过氧化物酶的转变过程可能涉及相似的结构变化。
