Pythocholic acid

The boa constrictor and python (species Boidae) are unique in that the major bile acid is pythocholic acid (3a,12a,16a-trihydroxy-5/8-cholanic acid) along with varying... 

Two unusual processes occur in the liver of these snakes 12a-hydroxylation of chenodeoxycholate to form cholate and 16 -hydroxylation of deoxycholate to produce pythocholate. Labeled cholesterol afforded labeled cholic and chenodeo-xycholic acids, but not labeled pythocholic acid. Labeled pythocholic acid was obtained following administration of labeled deoxycholate. There was evidence for the presence of a radiometabolite corresponding to 3a,12a-dihydroxy-16-oxocho-lanic acid in feces after oral administration of labeled cholesterol, cholic or de-oxycholic acid, but the material was absent from bile [147]. 

A few other compounds found in bile of specific animal species should be mentioned briefly. Hammarsten (39) isolated a substance from walrus and sea-lion bile that he showed to be a trihydroxy C24 acid. Windaus and Van Schoor (40) showed this to be an a-hydroxy acid, 3,7,23-trihydroxy-cholanic acid. This compound is called jS-phocaecholic acid. Pythocholic acid (C24H40O5) occurs in the bile of the family of snakes that includes boas and pythons (41, 42). The formula 3a,12a,16a-trihydroxycholanic acid has been suggested (43). Ursodeoxycholic acid (44) occurs in bear bile and is apparently 3a,7 -dihydroxycholanic acid. Hyodeoxycholic acid (3a,6a-dihydroxycholanic acid) has been isolated from hog bile. 

Pythocholic acid has been isolated from several species of snakes of the family Boidae (132). It was characterized as a 3-, 12-, 15- or 16-trihydroxy-cholanic acid by Haslewood and Wootton (132) and Haslewood (133). The assignment of the 16a-hydroxyl group is consistent with optical rotation data (134). The acid takes its name from the python where it is the principal bile acid. Despite its character as a unique trihydroxycholanic acid, pythocholic acid is probably not a primary acid, but rather formed by hydroxylation of deoxycholic acid returning from the gut (135). 

Myxinol is a unique tetrahydroxy bile alcohol that occurs in the bile of the hagfish, a most primitive marine cyclostome. It has not been detected in the bile of other species. The structure of myxinol recently clarified by Anderson et al. (232) bears resemblance to other bile salts but offers no promise of metabolic relationship with other known structures. It is conjugated with two moles of sulfate. The hydroxyl group at carbon 3 is, 3 the hydroxyl at carbon 16 is reminiscent of pythocholic acid. Unlike pythocholic acid, myxinol has the A/B trawy-conformation and contains other hydroxyl groups at carbons 3 and 7 rather than at carbons 3 and 12. 

Constrictor and python snakes have a capacity for the formation of pythocholic acid (3a, 12a, 16a-trihydroxycholanic acid) (Fig. 4) from deoxycholic acid in the liver. From an elaborate study with a bile fistula python and labeled cholesterol, Bergstrom et al. (1960a) showed the step-wise hydroxylation of the sterol nucleus to be 7a and then 12a. The 7a-hydroxyl group is lost through dehydration by the action of intestinal microorganisms and the deoxycholic acid subsequently formed is 16a-hydroxylated in the liver to pythocholic acid. 

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