326 CHOH HAO LI [18 



sequences in the polypeptide chains. Moreover, recent investigations with 

 T. Hayashida showed that whale, monkey and human somatotropins are 

 immunologically distinct from the bovine hormone (Table 13). On the other 

 hand, bovine somatotropin cannot be differentiated from the ovine hor- 

 mone by the precipitin test. 



Table 13 



PRECIPITIN TEST OF VARIOUS GROWTH HORMONES WITH 

 RABBIT ANTI-SERUM* TO BOVINE GROWTH HORMONE 



All somatotropins could be hydrolyzed partially with chymotrypsin with- 

 out inactivation. The extent to which hydrolysis of these five somatotropins 

 could be carried out with no loss of growth-promoting activity decreases 

 in the following order: Bovine, sheep, whale (25%)> monkey (20%)> human 

 (10%). Studies on the rate of chymotryptic digestion of these hormones of 

 the various species indicate that human somatotropin is the most resistant 

 to the enzyme action whereas bovine hormone is the most susceptible.^" 

 These differences in kinetic behavior in the course of enzymic hydrolysis 

 may also be taken as an indication of dissimilarity in composition and 

 structure. These observations provide an additional instance of the fact that 

 somatotropin molecules from various species differ completely from one an- 

 other with respect to chemical and structural characteristics. The hormones 

 from all species are equally active, however, in promoting growth in rats, 

 whereas only monkey and human hormones are effective in man.f Does 

 this mean that the rat is capable of degrading the bovine or ovine hormone 

 to the active core, whereas humans do not possess this ability? If this were 

 true, one might then assume that all somatotropins possess an identical core 



* Anti-serum to bovine growth hormone was obtained by immunizing rabbits as fol- 

 lows: Rabbits were injected subcutaneously with 5 mg. antigen in 1 ml. adjuvant (Bayol- 

 Arlacel) and 5 mg. antigen in 1 ml. saline once weekly for 3 weeks. After no injections for 

 3 weeks, the same injection schedule was followed for another 3 weeks. After no injections 

 for another 3 weeks, the same injection schedule was followed for only two weeks. After 

 no injections for another 3 weeks, the rabbits were bled by cardiac puncture. For pre- 

 cipitin tests, 0-1 ml. anti-serum was employed together with 0-5 ml. saline containing the 

 antigen. 



f Whether or not whale somatotropin exercises growth-promoting activity in man 

 remains to be investigated. From structural considerations, the whale hormone might 

 be expected to be active in human subjects. 



