18 II. BIOSYNTHESIS 



as a new formation of phospholipid when phosphate is present. The syn- 

 thesis of fat from carbohydrate is also a function of adipose tissue itself, 

 although acetate has not been shown to be an intermediate in this case.^^ 

 However, the addition of pyruvate or of acetate to retroperitoneal adipose 

 tissue of rats was shown by Haugaard and Marsh^^ to elevate the R.Q. 

 above unity; this phenomenon is interpreted as indicative of fat synthesis. 

 Sperry and co-workers^^ reported that, when octanoic acid-l-C^'* was per- 

 fused through rat brains, all lipid fractions except cholesterol contained 



Of all the extrahepatic tissues which bring about fat synthesis, mammary 

 tissue has been shown to be the most important. This is particularly 

 true in the case of ruminants, especially during the period of lactation. 

 Employing a direct approach to the problem, Zelter^'* reported that the 

 administration of acetate to a lactating cow increased lipid production in 

 the mammary gland, while butyric acid caused no significant change in 

 lipogenesis, unless given in conjunction with pyruvic acid or acetate. 



The ability of the mammary tissue to synthesize fatty acids from acetate 

 varies with the species. On the one hand, Folley and French^^'^^ found that 

 surviving udder slices of the lactating cow, goat, and sheep actively utilize 

 acetate as the sole substrate with an R.Q. exceeding unity. These data 

 were logically interpreted to mean that the ruminant mammary gland is 

 able to convert acetate into fatty acids; the short-chain acids in the newly 

 synthesized fat would represent an intermediate stage in the synthesis of 

 long-chain acids. 



On the other hand, acetate cannot be used for fat synthesis by the mam- 

 mary tissue of such non-ruminants as the rat, mouse, rabbit, or guinea 

 pjg 65,67 unless glucose is simultaneously present. This is in line with the 

 earlier results of Bloch and Kramer,^^ who demonstrated that acetate could 

 not be employed by liver slices for fat synthesis unless glucose was also in 

 the medium. Fat synthesis can readily be demonstrated in slices of 

 lactating rat udder when glucose is the substrate.®^ Acetate utilization 

 in sheep mammary tissue is likewise increased by this monosaccharide.^" 



61 E. Wertheimer and B. Shapiro, Physiol. Revs., 28, 451-464 (1948). 



62 N. Haugaard and J. B. Marsh, /. Biol Chem., 194, 33-40 (1952). 



" W. M. Sperry, R. M. Taylor, and H. L. Meltzer, Federation Proc, 12, 271-272 

 (1953). 



««Z. Zelter, Comvt. rend., 231, 1574-1576 (1950); 234, 567-569 (1952). 

 66 S. J. Folley and T. H. French, Biochem. J., 46, 465-473 (1950). 



66 S. J. FoUey and T. H. French, Nature, 163, 174-175 (1949). 



67 S. J. Folley and T. H. French, Biochem. J., 45, 117-125 (1949). 



68 K. Bloch and W. Kramer, /. Biol. Chem., 173, 811-812 (1948). 



69 J. H. Balmain, S. J. Folley, and R. F. Glascock, Nature, 169, 447-449 (1952). 



™ J. H. Balmain, S. J. Folley, and R. F. Glascock, Biochem. J., 52, 301-306 (1952). 



