Levine W G, Lu A Y
Drug Metab Dispos. 1982 Mar-Apr;10(2):102-9.
The metabolism of N,N-dimethyl-4-aminoazobenzene (DAB) was investigated in vitro by use of hepatic 10,000g supernatant fraction, microsomes, and purified cytochromes P-450 prepared from rats. Position-selective metabolism was studied in response to induction by 3-methylcholanthrene (MC), phenobarbital (PB), beta-naphthoflavone (BNF), and pregnenolone-16 alpha-carbonitrile (PCN) as well as inhibition by SKF 525-A, metyrapone, alpha-naphthoflavone, and piperonyl butoxide. The principal phase I pathways are demethylation of the tertiary (DAB) and secondary (MAB) amines and ring hydroxylation. When metabolism was measured with 10,000g supernatant fractions, each pathway responded differently and often independently to the inducers and inhibitors, suggesting that they are catalyzed preferentially by different isozymes of cytochrome P-450. Microsomes from PB-treated animals demethylated and hydroxylated DAB at the same rate as did control microsomes, based on cytochrome P-450 content, whereas microsomes from BNF- or MC-treated animals demethylated more rapidly and hydroxylated more slowly. Microsomes from PB-treated animals demethylated the secondary amine, MAB, more rapidly than the tertiary amine, DAB. Purified cytochrome P-448 from MC-treated animals catalyzed DAB demethylation very readily but hydroxylation very poorly. The turnover number was 10 times that seen in microsomes from MC-treated animals. Only one of the four cytochrome P-450 fractions isolated from PB-treated animals had significant activity with DAB and the turnover number of one of these (fraction B) was approximately that seen in microsomes. This study supports the concept of selectivity of various isozymes of cytochrome P-450 for the different steps in phase I metabolism of DAB. Furthermore, it is apparent that the association of certain inhibitors with specific isozymes of cytochrome P-450 is a generalization that requires qualification in terms of the substrates(s) involved.
利用大鼠肝脏10,000g上清液组分、微粒体和纯化的细胞色素P-450，在体外研究了N,N-二甲基-4-氨基偶氮苯（DAB）的代谢。研究了3-甲基胆蒽（MC）、苯巴比妥（PB）、β-萘黄酮（BNF）和孕烯醇酮-16α-腈（PCN）诱导以及SKF 525-A、甲吡酮、α-萘黄酮和胡椒基丁醚抑制对位置选择性代谢的影响。I相主要代谢途径是叔胺（DAB）和仲胺（MAB）的去甲基化以及环羟基化。当用10,000g上清液组分测定代谢时，每种途径对诱导剂和抑制剂的反应不同，且通常是独立的，这表明它们优先由细胞色素P-450的不同同工酶催化。基于细胞色素P-450含量，PB处理动物的微粒体使DAB去甲基化和羟基化的速率与对照微粒体相同，而BNF或MC处理动物的微粒体去甲基化更快，羟基化更慢。PB处理动物的微粒体使仲胺MAB去甲基化的速度比叔胺DAB更快。从MC处理动物中纯化的细胞色素P-448非常容易催化DAB去甲基化，但羟基化能力很差。周转数是MC处理动物微粒体中的10倍。从PB处理动物中分离出的四种细胞色素P-450组分中，只有一种对DAB具有显著活性，其中一种（组分B）的周转数与微粒体中的大致相同。本研究支持细胞色素P-450的各种同工酶对DAB I相代谢不同步骤具有选择性的概念。此外，显然某些抑制剂与细胞色素P-450特定同工酶的关联是一种普遍现象，但需要根据所涉及的底物进行限定。
