LIPIDS 155 



strongest evidence for this supposition is in the finding by Webley and 

 others (544) that the oxidation of ^-substituted phenyl fatty acids by 

 Nocardia opaca, an actinomycete, yields end products in conformity 

 with predictions based on /J-oxidation. Comparable studies on the 

 fungi have not yet appeared. 



Indirect evidence for /^-oxidation in the fungi is provided by the 

 incorporation of fatty acid carbon into the side chain of penicillin 

 (380, 516). The most effective precursors are fatty acids which by 

 their structure are not susceptible to complete /3-oxidation. 



It has been argued from simultaneous adaptation experiments that 

 Streptomyces aureofaciens oxidizes octanoate by some mechanism 

 other than /3-oxidation (276). However, it is now known that the 

 adaptation technique is unreliable in fatty acid oxidation, since the 

 adaptive system may be that which activates the fatty acid; failure of 

 octanoate-adapted cells to oxidize butyrate may therefore mean only 

 that activation of the two acids is carried out by different enzymes. 



Fatty acid oxidase systems probably occur in fungi and actinomy- 

 cetes (387, 543). In addition, mycelial extracts of Penicillium glaucum 

 and of Aspergillus spp. contain a lipoxidase, capable of oxidizing un- 

 saturated fatty acids (387). 



The Metabolism of Steroids and Triterpenes. Sterols occur in 

 small amounts in the lipid fraction of most fungi; ergosterol appears 

 to be the compound of this group most often formed by fungi, but 

 other sterols have been tentatively identified (Chapter 2). Cultural 

 conditions which favor sterol formation are reviewed by Bernhauer 

 (50). It appears that sterol and fat synthesis are competitive reactions; 

 the effect of pH on their formation (428) is perhaps the strongest 

 evidence for this competition. Biochemical studies on yeast and on 

 fungi indicate that ergosterol is formed in large part from 2-carbon 

 compounds, although isovaleric acid may also be involved (146, 318, 

 407). The amount of sterol formed varies among strains and among 

 single spore cultures of a given strain (556). 



The breakdown of exogenously supplied steroids has been studied 

 in two connections: (1) the utilization of steroids for energy and 

 carbon, and (2) partial and limited transformations of the steroid 

 molecule. 



Cholesterol is oxidized in soil (521) by actinomycetes and by Gram- 

 negative bacteria; it is not clear which organisms are responsible for 

 steroid breakdown in natural soils (462, 523, 525). Some fungi are 

 apparently able to grow with ergosterol as carbon source (462), and 

 some of the products of the action of Proactinomyces erythropolis on 



