Thesis Title

The Biosynthesis of Bile Acids in the Fire-Bellied Toad, Bombina Orientalis

Author

Kaiyan Tang

Date of Graduation

Fall 2003

Degree

Master of Science in Chemistry

Department

Chemistry

Committee Chair

Dean Cuebas

Subject Categories

Chemistry

Abstract

The ability of liver peroxisomes from the toad Bombina orientalis to metabolize several presumed intermediates during the biosynthesis of bile acids was investigated. Our hypothesis was that Bombina orientalis secrete almost exclusively (24R,25R)-3α, 7α, 12α, 24ζ-tetrahydroxy-5ß-cholestanoic acid as the primary bile because of a lack of dehydrogenase activity in the multifunctional enzyme known to be necessary for the synthesis of mature C24 bile acids. The enzymes peroxisome-enriched liver fractions efficiently hydrated (24E)-3α, 7α, 12α-trihydroxy-5ß-cholest-24-enoyl-CoA to 3α, 7α, 12α, 24ζ-tetrahydroxy-5ß-cholestanoyl-CoA, and also were able to dehydrogenate this intermediate to the 24-keto-3α, 7α, 12αζ-tetrahydroxy-5ß-cholestanoyl-CoA. The hydration products were predominantly the (24R,25R) and 24S,25S) stereoisomers of 3α, 7α, 12α, 24ζ-tetrahydroxy-5ß-cholestanoyl-CoA, as determined by retention time on high performance liquid chromatography. This result suggests that the peroxisomes of Bombina orientalis contain both multifunctional enzymes, MFE1 and MFE2, and that both the hydratase and dehydrogenase domains of MFE2 are active. Taken together, the results suggest that the reason why Bombina orientalis secrete almost exclusively (24R,25R)-3α, 7α, 12α, 24ζ-tetrahydroxy-5ß-cholestanoic acid as the primary bile acid remains elusive, and is not due to a lack of the dehydrogenase component of MFE2 and therefore our hypothesis must be rejected.

Copyright

© Kaiyan Tang

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