ISSN:0360-2532    

DOI:10.3109/03602538909103553

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

ISSN:0360-2532    

DOI:10.3109/03602538909103554

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractGenerally, most enzymes have a high degree of substrate specificity. In contrast, one of the primary characteristics of the cytochrome P-450s is a lack of substrate specificity. Specific isozymes will not only oxidize a number of different substrates but will often transform a single substrate into a number of different products. Indeed, it appears that almost any organic molecule that can reach the active site of the enzyme will be oxidized. This high degree of chemical reactivity demands that there must be some structural feature that controls access to the active site in order to prevent excess turnover of endogenous substances critical to the normal functioning of the organism. The structural feature that serves this role is the lipoidal character of the enzyme complex which results from the fact that it is membrane bound. Thus, the known endogenous substrates for the cytochrome P-450s, the steroids, prostaglandins, and fat-soluble vitamins, are all highly lipophilic substances.

ISSN:0360-2532    

DOI:10.3109/03602538909103555

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractOne major reason for determining the amino acid sequence of proteins comprising the liver microsomal hydroxylase system is to be able to apply the sequence data together with methodologies for isolating peptide fragments toward elucidation of their orientation in the membrane. In earlier reports we described the isolation and determination of the complete primary structure of several liver microsomal cytochromesb, [1-4], P-450 [5-8], epoxide hydrolase [9], and cytochromeb5reductase [10]. More recently the complete amino acid sequence of microsomal stearyl-CoA desaturase [11]and the 60-kDa membrane esterase [12] was also reported. Although much is known about the molecular properties and pharmacology of monooxygenase proteins, only a limited number of studies have been done to elucidate the orientation of these proteins in the endoplasmic reticulum.

ISSN:0360-2532    

DOI:10.3109/03602538909103556

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractAromatase, a cytochrome P-450, catalyzes the formation of aromatic C18 steroids from C19 androgens. The conversion reaction consists of complex processes which involve oxidative removal of the angular C-19 methyl group as formic acid and subsequent aromatization of the A ring (Fig. 1). Three moles each of NADPH and O2are consumed for each mole of estrogen formed. This enzyme has received considerable attention because of the central importance of estrogens in many reproductive and metabolic processes. A more detailed understanding of the role of this enzyme in steroidgenic metabolism has necessitated characterization of the protein at a molecular level.

ISSN:0360-2532    

DOI:10.3109/03602538909103557

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

ISSN:0360-2532    

DOI:10.3109/03602538909103558

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractIt was surprising to us to discover that testosterone could be converted to 17/3-hydroxy-4,6-androstadiene-3-one (Δ6-T) by liver microsomes from adult male rats [1], because at that time aromatase, which converts 4-androstene-3,17-dione to estrone [2], was the only isozyme of cytochrome P-450 known to catalyze the desaturation of an aliphatic substance. Subsequently, however, it was also discovered that the isozymes of cytochrome P-450 could also catalyze the desaturation of valproic acid to valproic-4-ene [3]. The ability of liver microsomes from rats to formΔ6-T was greatly increased by pretreating the rats with phenobarbital, pregnenolone-16a-carbonitrile, or dexamethasone. Indeed, the increases inΔ6-T formation were directly proportional to the increases in the formation of 6β-hydroxytestosterone, thereby suggesting that those isozymes that catalyze 6β-hydroxylation of testosterone were also able to catalyze the formation of A6-T but at much slower rates (approximately 10%).

ISSN:0360-2532    

DOI:10.3109/03602538909103559

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

ISSN:0360-2532    

DOI:10.3109/03602538909103560

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

ISSN:0360-2532    

DOI:10.3109/03602538909103561

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

ISSN:0360-2532    

DOI:10.3109/03602538909103562

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor