Biasutti M A, Posadaz A, García N A
Dpto. de Química, Universidad Nacional de Río Cuarto, 5800-Río Cuarto, Argentina.
J Pept Res. 2003 Jul;62(1):11-8. doi: 10.1034/j.1399-3011.2003.00064.x.
Kinetic aspects of the sensitized photooxidation of alpha- and beta-chymotrypsins have been studied at pH 6 and 8. The sensitization, employing classical O2(1Deltag)-photogenerators, such as xanthene dyes, is a kinetically intricate process because of the presence of ground state dye-protein associations and to the simultaneous participation of superoxide ion and singlet molecular oxygen [O2(1Deltag)]. Both proteins, that possess the same distribution pattern of photooxidizable amino acids, suffer a pure O2(1Deltag)-mediated photodynamic attack, using the carbonylic sensitizer Perinaphthenone. Overall and reactive rate constants for the O2(1Deltag)-quenching (in the order of 108 and 107/M/s, respectively), and rates of oxygen consumption determined by time-resolved, spectroscopic and polarographic methods indicate that alpha- and beta-chymotrypsins are less photooxidizable at pH 6, as a result of an enhancement of the O2(1Deltag)-physical quenching component. In general terms, beta-chymotrypsin exhibits the greater overall proclivity to interact with O2(1Deltag), whereas structural factors, possibly evidenced by a higher exposure of the reactive tryptophan residues, impart an increased photooxidation degree to the proteins at pH 8, specially to the alpha-chymotrypsin.
已在pH 6和pH 8条件下研究了α-和β-胰凝乳蛋白酶敏化光氧化的动力学方面。使用经典的O₂(¹Δg)光生成剂（如呫吨染料）进行敏化，由于存在基态染料-蛋白质缔合以及超氧离子和单线态分子氧[O₂(¹Δg)]的同时参与，这是一个动力学复杂的过程。两种蛋白质具有相同的可光氧化氨基酸分布模式，使用羰基敏化剂苊醌时，它们都遭受纯O₂(¹Δg)介导的光动力攻击。O₂(¹Δg)猝灭的总速率常数和反应速率常数（分别约为10⁸和10⁷/M/s），以及通过时间分辨、光谱和极谱方法测定的耗氧速率表明，由于O₂(¹Δg)物理猝灭成分的增强，α-和β-胰凝乳蛋白酶在pH 6时较不易被光氧化。一般来说，β-胰凝乳蛋白酶表现出与O₂(¹Δg)相互作用的总体倾向更大，而结构因素（可能表现为反应性色氨酸残基的更高暴露）在pH 8时使蛋白质的光氧化程度增加，特别是对α-胰凝乳蛋白酶。
