III. BIOCHEMICAL SYSTEMS 



277 



of mixed acids or oils can be used as a measure of the unsaturation. A few 

 important physical and chemical properties are summarized in Table I. 



TABLE I 

 Physical and Chemical Properties of the Essential Fatty Acids 



III. Biochemical Systems 



RALPH T. HOLMAN 



The biological role of the essential fatty acids has not yet been elucidated, 

 and only a few pieces of isolated information bear on the matter. The poly- 

 unsaturated acids present in animal tissues are found in greater concentra- 

 tion in the phospholipids than in the depot fats,^ • ^ and the concentration of 

 these acids in the total fatty acids of the so-called vital tissues is greater 

 than in the remainder of the carcass or in skeletal muscle. Changes m phos- 

 pholipid unsaturated fatty acids are greater than corresponding changes in 

 neutral fat fatty acids caused by fat deficiency or supplementation. It 

 appears that these substances are associated with tissue structural elements 

 rather than depot lipids, for alkaline hydrolysis of the tissues gives greater 

 yield of these acids than does exhaustive extraction with solvents. 



A study of the effects of fat deficiency upon enzyme systems should re- 

 veal some information about the metabolic role of the essential fatty acids. 

 Thus far the effects upon a few enzyme systems have been reported. Hess 

 and Violler* found that lipase activity in blood of rats decreases to about 

 half of normal on a fat-deficient diet, but that cholinesterase activity 

 remained unchanged. Kunkel and Williams'* found that fat deficiency caused 

 an increase in liver cytochrome oxidase activity and an increase in endogen- 

 ous respiration, whereas succinoxidase activity remained normal. They 



1 I. G. Rieckehoff, R. T. Holman, and G. O. Burr, Arch. Biochem. 20, 331 (1949). 



2R. Reiser, J. Nutrition 42, 325 (1950). 



3 W. Hess and G. Viollier, Helv. Chim. Acta 31, 381 (1948). 



^H. O. Kunkel and J. N. Williams, /. Biol. Chem. 189, 755 (1951). 



