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Enzymatic regulation of bile acid synthesis

1971; Elsevier BV; Volume: 51; Issue: 5 Linguagem: Inglês

10.1016/0002-9343(71)90282-8

1555-7162

G.S. Boyd, I W Percy-Robb,

Cholesterol and Lipid Metabolism

The conversion of cholesterol to bile acids involves the participation of various types of enzymes. These include different mono-oxygenases, dehydrogenases, isomerases, reductases, etc., together with various co-factors such as reduced nicotinamide adenine dinucleotide phosphate (NADPH), nicotinamide adenine dinucleotide (NAD+) and coenzyme A (CoA-SH). The activity of any one of the enzymes or the availability of a specific co-factor could in theory exert control over the fairly lengthy metabolic pathway between the C27 sterol and the C24 carboxylic acid. However, as few of the intermediates on this metabolic pathway ever accumulate to sizeable proportions under physiologic circumstances, this suggests that perhaps the rate-limiting event in the catabolic process may be the first reaction. Some of the evidence pointing to the role of the monooxygehase cholesterol-7α-hydroxylase as a possible rate-limiting enzyme in this connection is reviewed herein. The rate of turnover of this putative key enzyme is rapid, its rate of synthesis is influenced by the hepatic concentration of the end product of the over-all sequence (bile salt), but the precise mechanism by which this control is exerted remains obscure and is a challenge for future research.