Shah M A, Bergethon P R, Boak A M, Gallop P M, Kagan H M
Department of Biochemistry, Boston University School of Medicine, MA 02118.
Biochim Biophys Acta. 1992 Oct 20;1159(3):311-8. doi: 10.1016/0167-4838(92)90061-h.
Various o- and p-quinones were assessed as oxidants of peptidyl lysine in elastin and collagen substrates in the presence and absence of divalent copper as paradigms of protein-lysine 6-oxidase (lysyl oxidase) which contains both quinone and copper cofactors. Pyrroloquinoline quinone was among the most active in the absence and the most active of the o- and p-quinones tested in the presence of copper. The optimal rate of elastin oxidation occurred at a 2:1 PQQ/Cu(II) ratio while Cu(II) itself oxidized elastin relatively slightly. Elastin oxidation by 2:1 PQQ/Cu(II) required aerobic conditions consistent with oxygen-dependent turnover of this catalytic pair. Dimethylsulfoxide and catalase individually or in combination inhibited elastin oxidation by PQQ/Cu(II) by approx. 50%, suggesting that oxygen free radical species participate in the reaction. Amino-acid analysis of elastin and collagen substrates oxidized by 2:1 PQQ/Cu and then reduced with borohydride revealed that alpha-aminoadipic-delta-semialdehyde and lesser amounts of covalent cross-linkages were generated by this oxidant. In contrast, lysine oxidase produced aldehydes and significantly greater quantities of cross-linkage products, consistent with the known specificity of the enzyme. These data, thus, indicate the potential for free quinones, such as PQQ, particularly when stimulated by appropriate metal ions, to act as adventitious oxidants of lysine side-chains in proteins.
在有和没有二价铜存在的情况下，评估了各种邻醌和对醌作为弹性蛋白和胶原蛋白底物中肽基赖氨酸的氧化剂，以此作为蛋白质赖氨酸6-氧化酶（赖氨酰氧化酶）的范例，该酶同时含有醌和铜辅因子。吡咯喹啉醌在无铜时是活性最高的之一，在有铜存在时是所测试的邻醌和对醌中活性最高的。弹性蛋白氧化的最佳速率出现在PQQ/Cu(II) 比例为2:1时，而Cu(II) 本身对弹性蛋白的氧化作用相对较弱。2:1的PQQ/Cu(II) 对弹性蛋白的氧化需要有氧条件，这与该催化对的氧依赖性周转一致。二甲基亚砜和过氧化氢酶单独或联合使用时，可使PQQ/Cu(II) 对弹性蛋白的氧化作用受到约50% 的抑制，这表明氧自由基参与了该反应。对经2:1的PQQ/Cu氧化然后用硼氢化钠还原的弹性蛋白和胶原蛋白底物进行氨基酸分析，结果显示该氧化剂产生了α-氨基己二酸-δ-半醛和少量的共价交联产物。相比之下，赖氨酰氧化酶产生醛类和大量的交联产物，这与该酶已知的特异性一致。因此，这些数据表明游离醌（如PQQ）有潜力，特别是在受到适当金属离子刺激时，可作为蛋白质中赖氨酸侧链的偶然氧化剂。
