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18] STRUCTURE OF PITUITARY HORMONES 321 



Table 7 outlines the procedure for the isolation of growth hormone from 

 either monkey or human pituitary glands.'^"'' '^^ The primate somatotropins 

 have been assayed for their growth-promoting activity according to the 

 stimulation of the width of uncalcified tibial cartilage in hypophysectomized 

 rats, and their specific activities were found to be comparable to that of the 

 bovine hormone. '^'^^ As is to be expected, human and monkey growth hor. 

 mones cause a marked retention of nitrogen and phosphorous in patients 

 with mild hypopituitarism and in hypophysectomized male subjects.^^-^^ 



From sedimentation and diffusion data and from computed values for 

 partial specific volume,"^ the molecular weights for human and monkey 

 somatotropins were calculated to be 27,100 and 25,400 respectively. These 

 values differ greatly from the molecular weight of the bovine hormone.^" 

 Recently, Ehrenberg and Heijkenskjöld^* reported similar differences between 

 the molecular weights of human and bovine growth hormones. 



The electrophoretic mobihty of both human and monkey somatotropins 

 as a function of pH was determined in buffers of 0-1 ionic strength, and it 

 was found that the isoelectric point of the primate hormones is more acidic 

 than that of the bovine hormone.^" Table 8 summarizes some of the physico- 

 chemical properties of somatotropins isolated from monkey and human 

 pituitary glands. It may be seen that the monkey hormone contains four 

 residues of cystine, whereas the human contains only two. In this respect, 

 the monkey hormone is more like the bovine somatotropin. 



Table 8 



PHYSICOCHEMICAL CHARACTERISTICS OF 



GROWTH HORMONE ISOLATED FROM HUMAN 



AND MONKEY PITUITARY GLANDS 



From investigations of the N- and C-termini by both enzymic and chemi- 

 cal methods,^" -^^ it was postulated that both human and monkey somato- 

 tropins are composed of a single polypeptide chain with phenylalanine as 



* pK of phenolic group. 

 Wps 



