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7425927 
Journal Article 
Biotransformation of Bile Acids, Cholesterol, and Steroid Hormones 
Baron, SF; Hylemon, PB; , 
1997 
Springer US 
Boston, MA 
Gastrointestinal Microbiology 
470-510 
Steroids are a family of organic compounds that have a five-ring perhydrocyclo-pentanophenanthrene nucleus. The numbering system and skeletal structures for steroids are shown in Figure 13.1. Steroids vary in the number and location of double bonds; in the type, number, and position of functional groups; and in the stereochemical configuration of substituents below (α) or above (ß) the plane of the nucleus. Most steroids have 18ß- and 19 ß-methyl groups bonded to C-10 and C-13. The hydrogen atom in steroids saturated at at C-5 can be ß-oriented or α-oriented (allo). Alkyl side chains with various functional groups can be present at C-17, usually in the 17 ß orientation.