376 



CELLS, TISSUES, AND ORGANISMS 



the Specific activity of the medium was kept constant. This observation 

 implies that the more fatty acid presented to the muscle tissue, the 

 more fatty-acid carbon which finds its way into the protein. 



Growth hormone, then, as shown by these preliminary experi- 

 ments, may enhance the conversion of fatty-acid carbon to protein car- 

 bon by increasing the fatty-acid concentration in the extracellular fluid. 

 It may, in addition, exert an effect on the tissue, with a resulting stimu- 

 lation of palmitate-carbon incorporation into protein in the face of a 

 constant palmitate supply. This is suggested by the experiment illus- 

 trated in Table VH, which compared the incorporation of the labeled 

 palmitate carbon into the protein of diaphragms from hypophysecto- 

 mized and from hypophysectomized, growth-hormone-treated rats. 

 While the stimulatory effect of the growth-hormone treatment was not 

 large, it was statistically significant at the 5 per cent level. The possi- 

 bility remains, however, that these effects are artifacts explicable in 

 terms of dilution by the endogenous fatty-acid pool. Further experi- 

 ments taking this possibility into account are needed before definitive 

 interpretation is possible. 



The idea that the carbon of long-chain fatty acids may be incor- 

 porated into protein is given support by the finding of Manchester and 

 Young (1959b) and Manchester and Krahl (1959) that radiocarbon 

 from pyruvate, acetate, propionate, formate, a-ketoglutarate, citrate, 

 succinate, and even bicarbonate was incorporated into the protein of 

 isolated diaphragm and, more specifically, into the individual amino 

 acids of the protein, as revealed by degradation procedures. These 

 workers found in addition that insulin added to rat diaphragm in vitro 



TABLE VII 



Incorporation of C^'^ From Palmitate-1— C^"* into Protein of Isolated Rat Diaphragm 



Mean ± S.E.; number of observations in parentheses. 



