ff .Üf .9 $f # ^ * <»^- " # ü? ' ^ •*' 



18] STRUCTURE OF PITUITARY HORMONES 313 



and yet may have identical biological activity. Table 5 summarizes some 

 properties of pig corticotropin-A and sheep a-corticotropin. 



Table 5 

 SOME PROPERTIES OF CORTICOTROPINS 



A comparison of the amino acid sequences of both ^-MSH and the bovine 

 MSH with that of the corticotropins reveals that there is a central hepta- 

 peptide sequence that is common to both molecules : 



Corticotropins : Ser, 

 Melanotropins : . . . Pro. 



Tyr. 

 Tyr. 



Ser. 

 Lys. 



Met.Glu.Hls.Phe.Arg.Try.Gly. 

 Met.Glu.His.Phe.Arg.Try.Gly. 



Lys. 

 Ser. 



Pro. 

 Pro. 



Val. 

 Pro. 



It may also be noted that were it not for a transposition of the order of the 

 serines and lysines on either side of the heptapeptide core, the area of iden- 

 tity between the two hormones would extend to 11 amino acids. It appears 

 likely that the presence of this heptapeptide sequence in the corticotropins 

 explains their intrinsic melanocyte-stimulating activity. ^°§ Thus, it can be 

 postulated that it is by virtue of an arrangement of a different sequence of 

 amino acids on each side of the heptapeptide core that the molecule acquires 

 adrenal-stimulating as well as melanocyte-stimulating activity. 



* As trichloroacetate. 



t As acetate. 



% Minimum effective dose, 3-5 y/ 100 g. frog. 



§ Melanocyte stimulation is not the only function of a- ACTH in the absence of adrenal 

 glands. Recent studies of Menkin"'" have shown that the hormone peptide exerts a direct 

 local effect of repressing in an inflamed area the increased capillary permeability in adrena- 

 lectomized animals. In addition, it has been shown that the adipokinetic activity of a-ACTH 

 can be demonstrated in adrenalectomized mice maintained with corticoid therapy.^i 



