LIPIDS 153 



synthesis of esters, e.g., n-butyl oleate, from a fatty acid and an alcohol 

 (440). 



The phosphatides— lecithins and cephalins— are complex phospho- 

 lipids in which one of the fatty acids found in the true fats is replaced 

 by phosphoric acid linked to a nitrogen base. They are hydrolyzed, 

 at different points in the molecule, by the phospholipases A, B, and C 

 (498). Phospholipase A is found in Aspergillus oryzae (148) and 

 Lycoperdon giganteum (211), phospholipase B in the mycelium of 

 Penicillium notatum (191). Phospholipase C, identical with glycero- 

 phosphatase (Chapter 9), is found in a commercial enzyme preparation 

 from Aspergillus sp. (3). 



The Metabolism of Fatty Acids. The fatty acids occur both free 

 and combined in mycelium (Chapter 2); information on their bio- 

 synthesis has been summarized above. In this section we are con- 

 cerned with the breakdown of exogenous fatty acids, arising in natural 

 substrates by lipase action or supplied in pure culture as such. 



The breakdown of fatty acids in animal tissues is believed to occur 

 by the so-called "/^-oxidation-condensation" route: the oxidation pro- 

 ceeds by the removal of two carbon atoms at a time, with subsequent 

 recombination of the 2-carbon fragments to form acetoacetic acid. 

 Acetoacetate is formed by fungi during the oxidation of butyric acid 

 (149, 388), but the details of its origin are not known. We are con- 

 cerned, therefore, primarily with information bearing on the /3-oxida- 

 tion phase rather than on possible recombination processes. 



Beta-oxidation in animals is essentially the conversion of a fatty acid 

 of n carbon atoms (R— CH 2 — CH 2 — COOH) to one of n - 2 carbons 

 (R — COOH) and acetate or a derivative of acetate. The key inter- 

 mediate is a /?-keto fatty acid, and the reactions may be summarized as 

 follows: 



R _CH 2 — CH 2 — COOH -> R— CO— CH 2 — COOH (4) 



Fatty'acid /3-Keto acid 



R— CO— CH 2 — COOH -^ R— COOH + CH 3 COOH (5) 



Acetate 



Coenzyme A is required at two points: in the "activation" of the 

 original fatty acid, forming an acyl-coenzyme A, and in the formation 

 of acetate, which appears as acetyl-coenzyme A. Repetition of reac- 

 tions 4 and 5 leads ultimately to complete conversion of the long- 

 chain fatty acid to 2-carbon compounds. The process is reviewed in 

 detail by Green (245) and by Chaikoff and Brown (114). 



Evidence for /3-oxidation in fungi derives almost entirely from 

 studies on the breakdown of fats and fatty acids by growing or resting 



