The long range objective of this proposed research is to delineate the role of intestinal bacterial steroid biotransformations on overall human steroid metabolism. However, a more immediate objective is to test selected bile acid analogues as inhibitors of intestinal bacterial 7 Alpha and 7 Beta-dehydroxylase activity. The discovery of such inhibitors should theoretically make treatment of cholesterol gallstones by chenodeoxycholic acid or ursodeoxycholic acid more effective. The first aim will be to determine the mechanism(s) of inhibition of 7 Alpha and 7 Beta-dehydroxylase activity by bile acid oxazoline compounds in whole cells and cell extracts of Eubacterium sp. V.P.I. 12708. The second aim will be to elucidate the mechanism(s) of antibacterial activity of the bile acid oxazoline compounds. These compounds may be potentially useful growth permittants when substituted for antibiotics in animal feeds. The effectiveness of different bile acid oxazoline compounds against a number of physiologically different bacteria will be determined. The third aim will be to determine if mixed fecal becteria and rat hepatocyte monolayer cultures metabolize these steroids. Several additional bile acid analogues will be tested for their ability to inhibit 7 Alpha and 7 Beta-dehydroxylase activity as well as for their antibacterial activity. The fourth aim will be to purify and characterize 21-dehydroxylase from Eubacterium lentum V.P.I. 12708 using affinity chromatography techniques and to determine if this enzyme is linked to the oxixation of molecular hydrogen. The final aim will be to begin a study of the enzymology of cholesterol reduction by certain newly isolated Eubacterium species.