112 III. OXIDATION AND METABOLISM 



the striated muscle of the rabbit.-"'^ Brocklesby and Rogers-*^^ described 

 a substance in salmon liver and in pilchard oil which is very effective in de- 

 stroying vitamin A. Carter-^" found an enzyme in dogfish and halibut liver 

 oils which greatly reduced the vitamin A content. This might also be con- 

 sidered to be an unsaturated fatty acid oxidase. However, none of these 

 enzyme systems has been well characterized or prepared in reasonably pure 

 form. It is not certain whether or not any of these systems is identical with 

 soybean lipoxidase. 



(c) Acids Effective as Substrates. According to a number of investi- 

 gators,^'''''-"'"^^ only those acids which have an unsaturated hnkage in the 

 9 : 10 position are attacked by lipoxidase. However, since many of these 

 tests were made on impure substrates, the results are questionable. Holman 

 and Burr-^^ reported that crude extracts of lipoxidase attacked linoleic acid, 

 ethyl linoleate, linolenic acid, ethyl linolenate, and methyl arachidonate ; 

 it was later demonstrated that these essential acids were all oxidized at the 

 same rate.^^* 



Sunmer-i- j^g^^l suggested that the optimal molecular configuration for ac- 

 tivity was — CH:CH-CH2-CH:CH-(CH2)7-COOH, and that the double 

 bond nearer the carboxyl should probably have a cis configuration. This 

 hypothesis was based upon the fact that oleic acid, but not erucic acid (in 

 which no double bond occurs in the 9,10 position), was active. However, 

 since arachidonic acid has no double bond at position 9, it is evident that this 

 hypothesis must be modified. Bergstrom and Holman^^^ have indicated 

 that the configuration necessary for activity is the following: — CH:CH-- 

 CH2-CH:CH — , with both double bonds cis. This is in line with the find- 

 ings of Holman and Elmer^^* that only the cis isomers of linoleic and lin- 

 olenic acids serve as active substrates. Apparently, acids with conjugated 

 systems, as for instance, elaeostearic acid, are not attacked by lipoxi- 

 dase.^^^'^^^ Siillman^'^ reported that oxidation of linoleic acid by a lipoxi- 



** H. SiUlman, Personal communication (1947); cited by S. Bergstrom and R. T. 

 Holman, Advances in Enzymol., 8, 425-457 (1948), p. 443. 



209 H. N. Brocklesby, Fisheries Research Board, Can., Bull. No. 59, 1-431 (1941); with 

 N. I. Rogers, Ibid., Progress Repts., Pacific Coast Stas., 50, 4-8 (1941); Chem. Abst., 36, 

 2371 (1942). 



^'0 N. M. Carter, Fisheries Research Board, Can., Ann. Rept. 1941, Append. V; Rept. 

 Pacific Fisheries Exptl. Sta. (Prince Rupert, B.C.), 1941, 31-35. 



»ii H. A. Spoehr, J. H. C. Smith, H. C. Strain, and W. H. Mihier, Carnegie Inst. Wash. 

 Yearbook, 39, 147-154 (1940). 



212 R. J. Sumner, /. Biot. Chem., 146, 211-213 (1942). 



i"" R. T. Holman and G. O. Burr, Arch. Biochem., 7, 47-54 (1945). 



"* R. T. Holman and O. C. Elmer, /. Am. Oil Chemists' Soc, 24, 127-129 (1947). 



215 H. Siillman, Helv. Chim. Acta, 27, 789-793 (1944). 



216 H. Siillman, Helv. Chim. Acta, 24, 1360-1380 (1941). 



