LIPIDS 157 



2. Hydrogenation of steroid aldehydes or ketones by bacteria, yeast, 

 Streptomyces spp.. and Rhizopus nigricans. 



3. Hydrogenation of ring carbon atoms by Clostridium sp., Strepto- 

 myces sp., and Rhizopus nigricans. 



4. Dehydrogenation of steroid secondary alcohols b\ bacteria and 

 actinomycett^. 



5. Epoxydation ol steroids containing an isolated double bond, by 

 Curuularia lunata and Cunninghamella blakesleeana. 



6. Dehydrogenation in ring A. with or without degradation of the 

 side chain, by Fusarium solani, Calonectria decora, Cxlindrocarpon 

 radicola, and other fungi. 



7. Oxidation of the side chain only, e.g., by Gliocladium caten- 

 ulatiun. 



8. Ring cleavage with lactone formation, e.g., bv Pejiicilliufn 

 chrysogemim. 



Specific enzvme systems must, of course, be responsible for these 

 transformations, and some knowledge of animal and bacterial enzymes 

 is available (244, 577). The 6/3-hydroxylation of progesterone by 

 Aspergillus ochraceus is accelerated by zinc: it has been suggested that 

 the metal is required for the synthesis of an induced enzyme which 

 carries out the reaction (17- 



Steroidal sapogenins, e.g., diosgenin, appear not to be hydroxylated 

 by fungi or other microorganisms (376). 



Chemical studies on several basidiomycetes have brought to light a 

 new series of fungal metabolites, the tetracyclic triterpenes. As 

 terpenes they are related to the carotenoids, but their structure also 

 bears an obvious relation to that of the sterols; they are not, however, 

 true sterols. Similar compounds are known in higher organisms, e.g.. 

 betulin in plants and squalene in animals. The structure of eburicoic 

 acid, formed bv several Hxmenomvcetes (151, 220, 281), may be taken 

 as an example of the group: 



HOOC 



HO— 

 CI 



