278 ESSENTIAL FATTY ACIDS 



reported that choline oxidase activity rose slightly in the deficient state. 

 With the exception of choline oxidase, all enzyme systems reverted toward 

 normal activities upon the administration of linoleate to the deficient ani- 

 mals. Thus it appears that essential fatty acid is involved in at least some 

 enzyme systems. The lipid in concentrated cytochrome oxidase prepara- 

 tions has been found to contain polyunsaturated fatty acids, and the lipo- 

 protein of blood is subject to autoxidation, as are the polyunsaturated 

 acids, indicating that these acids occur in important lipoprotein structures. 

 The essential fatty acids are themselves the substrates for a highly specific 

 enzyme in the plant kingdom. The occurrence of this enzyme, lipoxidase, 

 in animal tissues is not conclusively established. For more detailed informa- 

 tion concerning this enzyme and its action, the reader is referred to several 

 reviews. ^'^ Lipoxidase attacks compounds in which there is multiple methyl- 

 ene-interrupted unsaturation of all cis configuration. The commonest and 

 simplest substrate is linoleate, containing the structure 



— CH 



II 

 CH— CH2— CH 



II 

 CH— 



This enzyme is of considerable importance in plant seeds where linoleic and 

 linolenic acids are storage materials, but it is doubtful that the lipoxidase is 

 of much metabolic importance in animal tissue if it exists there, for the 

 potential substrate is largely bound in structural lipid. 



IV. specificity of Action 



RALPH T. HOLM AN 



There has been considerable uncertainty over the comparative curative 

 values of the various fatty acids and over their minimum daily requirements. 

 Through the mass of collected information it is clear that the polyunsat- 

 urated fatty acids are divided into two classes: those that cure skin symp- 

 toms and restore growth, and those that restore growth but do not cure 

 skin symptoms. 



Linoleic and arachidonic acids both restore growth and cure skin symp- 

 toms. Turpeinen^ reported that arachidonic acid was three times as effective 



^S. Bergstrom and R. T. Holman, Advances in Enzymol. 8, 425 (1948). 



* R. T. Holman and S. Bergstrom, in The Enzymes, VoL 2, Part 1, Chapter 60. 



Academic Press, New York, 1951. 

 ^W. Franke, Fette u. Seifen 52, 11 (1949). 

 10. Turpeinen, /. Nutrition 15, 531 (1938). 



