5 p-CHOLESTANE · 3 a , 27-DIOL : NAD + OXIDOREDUCTASE AND 3 a-HYDROXY-5 p-CHOLESTAN-27-AL : NAD + OXIDOREDUCT ASE IN RAT LIVER EXTRACT * )
Using rat liver alcohol:NAD+ oxidoreductase and aldehyde:NAD+ oxidoreductase, the following facts were found: 1) 3a-hydroxy-5~-cholestan-27-al was reduced to 5fi -cholestane-3a, 27-diol by liver alcohol: NAD+ oxidoreductase. 2) The optimum pH was pH 7. 0 with potassium phosphate buffer and pH 8. 5 with Tris buffer. 3) The Km value of the substrate to the enzyme was 14. 3 μM. 4) 3a-Hydroxy5fi-cholestan-27al was oxidized to 3a-hydroxy5fi-cholestan27-oic acid by liver aldehyde: NAD+ oxidoreductase. 5) The optimum pH was pH 8. 5 with Tris buffer. 6) The Km value of the substrate to the enzyme was 26. 3 μM.
The formation of lithocholic acid, chenodeoxycholic acid and other bile acids from 3 beta-hydroxychol-5-enoic acid in vitro and in vivo.
Abstract Previous work has shown that 3β-hydroxycholenoic acid and several naturally occurring C 24 bile acids are formed from cholesterol incubated with rat-liver mitochondria. It is now shown that [ 3 H]3β-hydroxycholenoic acid is converted into lithocholic, chenodeoxycholic, 3α,6β-dihydroxycholanoic and β-muricholic acids in vitro . This suggests that 3β-hydroxycholenoic acid is an intermediate in the formation of C 24 bile acids from cholesterol in vitro . When [ 3 H]3β-hydroxycholenoic acid is injected intravenously into rats, 80% of the radioactivity is recovered in the bile within 2 h, mainly as lithocholic, chenodeoxycholic, 3α,6β-dihydroxycholanoic and β-muricholic acids. This raises the possibility that 3β-hydroxycholenoic acid lies on one of the pathways by which chenodeoxycholic acid is formed in vivo .
Oxidation of 5β-cholestane-3α,7α,12α-triol by rat-liver mitochondria
Abstract The oxidation of 5β-cholestane-3α,7α,12α-triol (an intermediate in the conversion of cholesterol to cholic acid) was studied. 1. 1. Experimental conditions for the study of the oxidation of 5β-cholestane-3α, 7α,12α-triol were established. 2. 2. When 5β-cholestane-3α,7α,12α-triol was incubated with rat-liver particulate fractions, the formation of 5β-cholestane-3α,7α,12α,26-tetrol and 5β-cholestane 3α,7α,12α-triol-26-oic acid was observed only in the incubation mixture containing mitochondria. 3. 3. The addition of boiled rat-liver extract to the incubation mixture greatly stimulated the production of 5β-cholestane-3α,7α,12α,26-tetrol, while 100000 × g supernatant did not show such a stimulative effect. 4. 4. Among the various animals studied, rats and mice showed the greatest activity for the oxidation of 5β-cholestane-3α,7α,12α-triol. 5. 5. Among the cofactors tested, only NADPH (an excess amount compared to that contained in boiled extract) could substitute for the boiled rat-liver extract in the oxidation of 5β-cholestane-3α,7α,12α-triol.