Structure, Function and Regulation of Lung-Specific Carbonyl Reductase

羰基还原酶(EC 1.1.1.184)是一种依赖NADPH的氧化还原酶，对羰基化合物具有广泛的专一性。猪、小鼠和豚鼠的肺中特异地含有一种不同于其他哺乳动物组织中的单体酶的寡聚体羰基还原酶。在这项研究中，我们从这些动物的肺中纯化了低聚体羰基还原酶，并对其结构和功能特性、在肺中的定位以及效应器对酶活性的调节进行了研究，以阐明其在异源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，MR为103,000，由明显相同的MR 24,000亚基组成。利用肺酶的特异性抗体，从猪肺CDNA文库中分离到一个CDNA克隆，并测定了该克隆的核苷酸序列。用部分Se…验证了预测的氨基酸序列对酶蛋白进行了更多的频率分析，并定位了一个与许多其他依赖于吡啶核苷酸的脱氢酶相似的辅酶结合区。化学修饰研究表明，在酶的活性中心或附近存在必需的赖氨酰和组氨酸残基。功能。该酶还原了包括3-酮类固醇和脂肪醛在内的各种脂肪族和芳香族羰基化合物，并将醛氧化为羧酸。免疫组织化学研究表明，该酶定位于这些动物肺的Clara细胞、纤毛细胞和II型肺泡细胞。因此，该酶可能在脂质过氧化、类固醇代谢、乙醚类脂生物合成以及药物代谢所产生的羰基化合物歧化中发挥作用。监管。该酶对羰基底物表现出负的协同作用。脂肪酸作为变构效应消除了这种负相互作用。尤其是油酸和花生四烯酸等顺式不饱和脂肪酸是最有效的激活剂，其KA值在2.2-14um之间。脂肪酸效应在脂肪酸合成醚脂的过程中可能起着重要的调节作用，脂肪酸的低Ka值提示该酶还有一种额外的功能，即该酶作为一种肺特异结合蛋白与脂肪酸结合。较少

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