?e .^ • i # 



18] STRUCTURE OF PITUITARY HORMONES 305 



two laboratories. "'^^'^"^ The data obtained by Harris and Roos^" and 

 Geschwind et al.^^'^^ are in complete agreement. Using techniques 

 developed for structural studies on insulin^^ and on the corticotropins,^" 

 both groups of investigators obtained the following amino acid sequence 

 for iS-MSH: 



H-Asp.Glu.Gly.Pro.Tyr.Lys.Met.Glu.His.Phe.Arg.Try.Gly.Ser.Pro.Pro.Lys.Asp-OH 

 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 



It has been shown that neither /3-aspartyl, nor y-glutamyl, nor e-amino 

 linkages occur in ^-MSH.^^ The two residues of aspartic acid that occur in 

 the peptide occupy the A^- and C-terminal positions in the chain. Hydro- 

 lysis of the hormone peptide with trypsin and chymotrypsin has been found 

 to proceed in accordance with the known specificity of these proteolytic 

 enzymes, with the one exception that the Lys. Asp linkage (positions 17-18) 

 is resistant to cleavage by trypsin. 



Although preparations of active MSH extracts from bovine pituitary have 

 been reported,^^-^^ the isolation of a bovine MSH in pure form has only 



Anode 



Fig. 2. Resolution of chymotryptic digest of beef /S-MSH by 

 paper electrophoresis in y-collidine-acetic acid buffer of pH 7-0; 

 11 v/cm. 



|Ch-5B 



Origin 

 Ch-4B 



Ch-3B 

 Ch-2B 



Cathode 



recently been achieved. ^2* The complete amino acid sequence of the bovine 

 MSH has now also been elucidated by various methods, as shown in Table 1. 

 It may be seen that the structure proposed for the bovine hormone differs 

 from that proposed for the pig jS-MSH only at position 2, where a seryl 



* Very recent investigations with I. I. Geschwind indicate that about 80% of the MSH 

 component isolated from sheep posterior-intermediate pituitaries is identical with the 

 bovine j8-MSH in both composition and the amino acid sequence, whilst the remaining 

 active material is identical with the pig hormone. 



Ups 



