Structure, Function and Regulation of Lung-Specific Carbonyl Reductase

羰基还原酶（EC 1.1.1.184）是对羰基化合物具有广泛特异性的几种NADPH依赖性氧化还原酶之一。猪、小鼠和豚鼠的肺特别地含有不同于其它哺乳动物组织中的单体酶的寡聚羰基还原酶。在本研究中，我们从这些动物肺中纯化了寡聚羰基还原酶，并对其结构和功能特性、在肺中的定位以及效应物对酶活性的调节进行了表征，以阐明其在外源性和内源性羰基化合物的肺代谢中的作用.结构肺羰基还原酶是一个四聚体，分子量为103，000，由分子量为24，000的表观相同亚基组成。用一种抗羰基还原酶的特异性抗体，从猪肺cDNA文库中分离到一个羰基还原酶cDNA克隆，并测定了该克隆的核苷酸序列。预测的氨基酸序列经部分测序证实 ...更多信息 序列分析的酶蛋白，也定位了一个假定的辅酶结合区类似于许多其他吡啶核苷酸依赖性的辅酶。化学修饰研究表明，在酶活性中心或附近存在必需的赖氨酰和组氨酰残基.功能该酶还原各种脂肪族和芳香族羰基化合物，包括3-酮类固醇和脂肪醛，并将醛氧化为羧酸。免疫组化结果显示，该酶定位于克拉拉细胞，纤毛细胞和II型肺泡细胞在这些动物的肺。因此，该酶可能在脂质过氧化、甾体代谢、醚类脂质生物合成以及药物代谢等羰基化合物歧化过程中发挥作用.调控该酶表现出负协同性相对于羰基底物。脂肪酸作为变构效应消除负相互作用。特别是，顺式不饱和脂肪酸如油酸和花生四烯酸是最有效的活化剂，其Ka值为2.2-14 μ M。脂肪酸效应可能是重要的，在由脂肪酸的醚脂质的合成的酶的调节，和低Ka值的脂肪酸建议的额外功能，该酶作为一个肺特异性结合蛋白的脂肪酸。少

Carbonyl reductase(EC 1.1.1.184)is one of several NADPH-dependent oxidoreductases having wide specificity for carbonyl compounds. Lungs of pig, mouse and guinea-pig specifically contain an oligomeric carbonyl reductase different from the monomeric enzymes in other mammalian tissues. In this study, we purified the oligomeric carbonyl reductase from these animal lungs, and characterized its structural and functional properties, localization in lung, and regulation of the enzyme activity by effectors, in order to elucidate its role in pulmonary metabolism of xenobiotic and endogenous carbonyl compounds.1. Structure. The pulmonary carbonyl reductase was a tetramer with a Mr of 103, 000, consisting of apparent identical subunits of Mr 24, 000. A CDNA clone for carbonyl reductase was isolated from a pig lung CDNA library by use of a specific antibody to the pulmonary enzyme, and the nucleotide sequence of the clone was determined. The predicted amino acid sequence was confirmed by partial se … More quence analysis of the enzyme protdin, and also localized a putative coenzyme binding region similar to that of many other pyridine nucleotide-dependent dehydrogenases. Chemical modification study suggested the presence of essential lysyl and histidyl residues at or near the active center of the enzyme.2. Function. The enzyme reduced various aliphatic and aromatic carbonyl compounds including 3-ketosteroids and fatty aldehydes, and oxidized aldehydes to carboxylic acids. Immunohistochemical study revealed that the enzyme was localized in the Clara cells, ciliated cells, and Type II alveolar cells in these animal lungs. Thus, the enzyme may play roles in dismutation of carbonyl compounds derived from lipid peroxidation, steroid metabolism, and biosynthesis of ether lipids, as well as drug metabolism.3. Regulation. The enzyme exhibited negative cooperativity with respect to the carbonyl substrates. Fatty acids acted as allosteric effectors abolishing the negative interaction. Especially, cis-unsaturated fatty acids such as oleic acid and arachidonic acid were most effective activators showing Ka values of 2.2-14 muM. The fatty acid effect may be important in the regulation of the synthesis of ether lipids from fafiy acids by the enzyme, and the low Ka values for the fatty acids suggests an additional function that the enzyme acts as a lung-specific binding protein for fatty acids. Less