24 



II. BIOSYNTHESIS 



distributed throughout the molecule. A similar result was obtained with 

 liver slices incubated with labeled acetate, as reported by Brady and 

 Gurin.9« 



The most convincmg evidence of the stepwise nature of the synthetic 

 process in the formation of fatty acids has come from the experiments of 

 the Popjak group^^ on lactating goats. After 5 mc. of carboxyl-labeled 



Experimental period I 



Experimental period H 



30 



20 



.0 ■ 



0.5 



ll 



2 4 6 8 10 12 14 16 18 18 



4 6 8 10 12 14 16 18 18 



i 



Length of carbon chain 



Fig. 1. Relationship between the specific activity and the chain length of the glyceride 

 fatty acids in the nailk of a goat injected with 5 mc. of carbo.xyl-labeled C'^ acetate. 

 Experimental period I represents the results of analyses of samples of milk fat col- 

 lected from 1 to 2 hours after the acetate injection. Experimental period II involves 

 analyses of samples collected from 12 to 48 hours after the acetate injection. The 

 symbol A^ over the last columns indicates oleic acid.^'*^ 



C'** acetate had been injected into a goat, the milk fatty acids were found 

 to contain increasing specific activities in a stepwise ratio from butyric 

 to palmitic (hexadecanoic) acids; on the other hand, the results on stearic 

 (octadecanoic) and oleic (9-octadecenoic) acids are entirely out of line 

 with those of the lower acids. A summary of the data from these experi- 

 ments is given in Figure 1. 



3«R. O. Brady and S. Gurin, /. Biol Chem., 186, 461-469 (1950). 

 " G. Popjdk, T. H. French, G. D. Hunter, and A. J. P. Martin, Biochem. J., 48, 

 612-618(1951). 



