HYDKOLYSIS PRODUCTS OF PHOSPHOLIPIDS 239 



pig brain. The parent substance was believed to be diphosphoinositide. 

 Although Streicher'^ indicated that the turnover of P^- in brain phospho- 

 lipid is notoriously slow, and is close to zero in the great bulk of such com- 

 pounds, it is suggested that it may be high in a small fraction or "trace" 

 compomid of the phospholipids. 



3. The Oxidation and IMetabolisni of Hydrolysis Products of Phos- 

 pholipids 



(1) Choline 



a. Introduction. At least two enzymes are concerned with the oxidation 

 of choline, namely choline oxidase (CO) and choline dehydrogenase (CD). 

 In addition to these, two other enzymes of importance in choline metab- 

 olism occur in rat liver, namely, betaine aldehyde dehydrogenase (BAD) 

 and sarcosine oxidase. Christensen and Daniel^'' demonstrated that cho- 

 line dehydrogenase and betaine aldehyde dehydrogenase are different en- 

 zymes, inasmuch as, on centrifugation of sucrose homogenates of rat liver, 

 CD was found chiefly in the mitochondrial fraction, while BAD remained 

 in the supernatant fraction. 



b. Choline Oxidase, (a) Distribution of Choline Oxidase. Bernheim 

 and Bernheim," in 1933, were the first to recognize that acetylchohne 

 could be oxidized by rat liver, and that one and one-half atoms of oxygen 

 were required for the change. The optimum pH was found to be 7.0, but 

 no enzyme was mentioned. Five years later, these workers^^ proved that 

 the destruction of choline was mediated by an enzyme, which they were 

 able to separate in relatively pure form. In the course of the oxidation, it 

 was fomid that choline is changed to betaine aldehyde, with the uptake of 

 one atom of oxygen, and then to betaine, with the incorporation of two 

 molecules of oxygen in the reaction. The enzyme differed from alcohol 

 oxidase, and was named "choline oxidase." Although Mann and Quastel,^' 

 in 1937, expressed some doubt whether or not the enzyme responsible for 

 the oxidation of choline was specific, these workers-^ came to the conclusion 

 in 1938 that a choline oxidase did exist in rat liver. It is thus evident that 



19 E Streicher, Federation Proc, 12, 139-140 (1953). 



2" J. R. Christensen and L. J. Daniel, Federation Proc, 12, 189-190 (1953). 

 21 F. Bernheim and M. L. C. Bernheim, Am. J. Physiol., 104, 438-439 (1933). 

 " F. Bernheim and M. L. C. Bernheim, Am. J. Physiol, 121, 55-60 (1938). 

 " P. J. G. Mann and J. H. Quastel, Biochem. J., 31, 869-878 (1937). 

 " P. J. G Mann, H. E. Woodward, and J. H. Quastel, Biochem. J., 32, 1024-1032 

 (1938). 



