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18] STRUCTURE OF PITUITARY HORMONES 323 



a highly purified state; this whale somatotropin was demonstrated to be 

 structurally more similar to primate hormones than to sheep or beef somato- 

 tropin. 



The procedure employed for the purification and isolation of whale somato- 

 tropin is essentially the same as those described for the bovine^^ and the 

 primate'^ -^^ hormones. Table 9 presents a summary of the average yield 



Table 9 



YIELD AND ACTIVITY OF FRACTIONS OBTAINED FROM THE 

 ISOLATION PROCEDURE OF WHALE GROWTH HORMONE 



and activity of fractions obtained from each step of the isolation procedure. 

 The pattern obtained when the somatotropin concentrate was submitted to ion 

 exchange chromatography can be seen in Fig. 1 1 ; the activity was found in 

 tubes 140 to 170. The purified product behaves as a homogeneous substance 

 when submitted to chromatographic analysis on the same resin (Fig. 11). In 

 addition, no evidence of heterogeneity was observed in the ultracentrifuge or 

 in free boundary electrophoresis. Terminal group analyses indicate that whale 

 somatotropin consists of one TV-terminal phenylalanine and one C-terminal 

 phenylalanine, in amounts consistent with a molecular weight of 39,900. 

 The isoelectric point has been determined in buffers of 0-1 ionic strength 

 and found to be located at pH 6-2. As is the case in the other somatotropins, 

 the integrity of the whole protein molecule is not essential for the growth- 

 promoting activity of whale somatotropin (Table 10). 



Highly purified preparations of growth hormones from five different 

 mammalian species are now available for study and comparison. Table 11 

 summarizes some physicochemical properties of these five somatotropins. 

 The molecular weights range from 25,000 for monkey growth hormone to 

 48,000 for the ovine hormone. Beef, sheep and whale growth hormones have 

 isoelectric points at pH 6-85, 6-8 and 6-2 respectively, while human and 

 monkey somatotropins are more acidic, with isoelectric points at pH 4-9 

 and 5-5 respectively. Both beef and sheep growth hormones are composed 



* Total dose in 4 days; tibia width in mean ± S.E.; tibia width for the controls, 160 /x. 



