Penning T M, Sharp R B
Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia 19104-6084.
Carcinogenesis. 1990 Jul;11(7):1203-8. doi: 10.1093/carcin/11.7.1203.
Dihydrodiol dehydrogenase (DD; EC 1.3.1.20) will oxidize non-K-region trans-dihydrodiols of polycyclic aromatic hydrocarbons (PAHs), a reaction that can suppress the formation of PAHs) anti-diol epoxides or ultimate carcinogens. Using benzenedihydrodiol [(+/-)-trans-1,2-dihydroxy-3,5-cyclohexadiene] as a model substrate for trans-dihydrodiol metabolites of PAHs, 23 human liver and eight human lung samples were examined for enzyme activity. In human liver, enzyme activity could be measured spectrophotometrically and specific activities ranged from 0.16 to 6.1 nmol benzenedihydrodiol oxidized min/mg protein. Western blot analysis of human liver cytosol using rabbit anti-rat DD serum detected two bands of mol. wts 34,000 and 27,000. The former mol. wt is identical to that observed for the homogeneous rat liver enzyme. Gel-filtration experiments indicate that human liver DD activity elutes as a single peak and co-elutes with the purified rat liver enzyme, suggesting that the lower mol. wt species may be an artefact of degradation. Preparations of the human liver enzyme required NADP- for activity and were in general, insensitive to inhibition by dicoumarol, indomethacin and 6-medroxyprogesterone acetate. These properties distinguish the enzyme from alcohol dehydrogenase, quinone reductase and rat liver DD. In human lung, DD activity was barely detectable using a sensitive radiochemical assay in which the oxidation of benzenedihydrodiol to catechol is linked to catechol-O-methyl transferase using [3H]S-adenosyl methionine as methyl donor. Specific activities were approximately 1000th of that observed for human liver and ranged from 1 to 4 pmol benzenedihydrodiol oxidized/min/mg protein. Western blot analysis of lung cytosol detected three bands of mol. wts 34,000, 31,000 and 28,000. The relatively high levels of DD in human liver suggest that this enzyme may play an important role in PAH detoxication in this organ, while the low levels of DD in lung may contribute to the susceptibility of this tissue to PAH-induced carcinogenesis.
二氢二醇脱氢酶（DD；EC 1.3.1.20）可氧化多环芳烃（PAHs）的非K区反式二氢二醇，该反应可抑制PAHs反式二氢二醇环氧化物或最终致癌物的形成。以苯二氢二醇[（±）-反式-1,2-二羟基-3,5-环己二烯]作为PAHs反式二氢二醇代谢物的模型底物，检测了23份人肝脏样本和8份人肺样本的酶活性。在人肝脏中，酶活性可用分光光度法测定，比活性范围为0.16至6.1 nmol苯二氢二醇氧化/分钟/毫克蛋白质。用人抗大鼠DD血清对人肝脏胞质溶胶进行蛋白质免疫印迹分析，检测到两条分子量分别为34,000和27,000的条带。前者的分子量与均一化大鼠肝脏酶的分子量相同。凝胶过滤实验表明，人肝脏DD活性以单峰形式洗脱，并与纯化的大鼠肝脏酶共洗脱，这表明分子量较低的条带可能是降解产物。人肝脏酶制剂的活性需要NADP⁺，并且一般对双香豆素、吲哚美辛和醋酸6-甲氧基孕酮的抑制不敏感。这些特性将该酶与醇脱氢酶、醌还原酶和大鼠肝脏DD区分开来。在人肺中，使用灵敏的放射化学测定法几乎检测不到DD活性，该测定法中苯二氢二醇氧化为儿茶酚的过程与儿茶酚-O-甲基转移酶相连，使用[³H]S-腺苷甲硫氨酸作为甲基供体。比活性约为人肝脏中观察到的比活性的千分之一，范围为1至4 pmol苯二氢二醇氧化/分钟/毫克蛋白质。对肺胞质溶胶的蛋白质免疫印迹分析检测到三条分子量分别为34,000、31,000和28,000的条带。人肝脏中相对较高水平的DD表明，该酶可能在该器官的PAH解毒中起重要作用，而肺中较低水平的DD可能导致该组织对PAH诱导的致癌作用易感。
