Physicochemical Studies of Xanthine Oxidizing Enzymes

96-03591 Massey 1.技术本研究者分离出了稳定状态的牛奶黄嘌呤脱氢酶，它可以可逆地转化为氧化形式，其中优选的电子受体是氧而不是NAD，因为它是脱氢酶形式。这项工作表明，这种可逆的相互转换，这是由氧化的空间相邻的巯基残基的脱氢酶氧化酶转化所带来的主要影响，涉及蛋白质的构象变化，主要影响黄素氧化还原中心。这项研究的主要目的是详细研究两种形式的酶的物理化学性质，目的是确定赋予两种形式不同催化性质的参数。这项研究涉及广泛使用的快速反应分光光度法，黄素替代研究，催化性质的酶与不同类别的底物，并检查的模式的结合和机制的有效抑制剂的酶。 2.黄嘌呤氧化酶能以两种催化性质截然不同的稳定形式存在，这使它成为一种非常不寻常的酶。人们普遍认为，这种相互转化形成了各种氧化应激现象的基础，因为氧化酶形式产生氧自由基的能力。为了评估这样的假设，有必要对这两种酶的性质有一个透彻的了解。本项目就是针对这样一项研究。

96-03591 Massey 1. Technical This investigator has isolated milk xanthine dehydrogenase in a stable state, which can be converted reversibly into the oxidized form, where the preferred electron acceptor is oxygen rather than NAD, as it is with the dehydrogenase form. This work indicates that the major effects of this reversible interconversion, which is brought about by oxidation of spatially adjacent thiol residues in the dehydrogenase to oxidase conversion, involve conformational changes in the protein which affect mainly the flavin redox center. The major thrust of this research is to study in detail the physicochemical properties of the two forms of the enzyme, with the aim of defining the parameters that give the two forms such different catalytic properties. This study involves extensive use of rapid reaction spectrophotometry, flavin replacement studies, catalytic properties of the enzymes with different classes of substrates, and examination of the modes of binding and mechanism of potent inhibitors of the enzymes. 2. Nontechnical The ability of xanthine oxidase to exist in two stable forms with very different catalytic properties makes it a very unusual enzyme. It is widely believed that this interconversion forms the basis of a variety of oxidative stress phenomena, because of the ability of the oxidase form to generate oxygen radicals. In order to assess such hypotheses, it is essential to have a thorough understanding of the properties of the two enzyme forms. This project is focused on such a study.