304 CHOH HAO LT [18 



of the epidermal melanophores. Subsequently, Allen^- and Swingle^^ showed 

 that transplantation of the intermediate lobe of adult frogs into normal or 

 hypophysectomized tadpoles induces a marked expansion of the melano- 

 cytes. It was further demonstrated^^ '^^ that extracts of the intermediate 

 lobes of the bovine pituitary exercised the most marked influence on the 

 pigmentation of the hypophysectomized tadpole, although suspensions of 

 the anterior lobes were also effective in this regard. These earlier investiga- 

 tions have left no doubt that the pituitary gland possesses a principle or 

 principles which regulate the pigmentation of amphibia. 



The main sources of starting material for the purification of the melanocyte- 

 stimulating hormone have been the posterior-intermediate lobes of beef and 

 pig pituitary glands. The pioneer studies of Hogben, Zondek, lores, Stehle, 

 Landgrebe, and their collaborators, have shown the hormone to be a poly- 

 peptide of comparatively low molecular weight. Since 1955, four groups of 

 investigators^^-^^'^'-^^-^^-^"'^^-^^ have published methods for the purification 

 and isolation of MSH from beef and pig pituitary glands. All the pubhshed 

 procedures for the preparation of MSH concentrates from either pig or beef 

 posterior-intermediate pituitaries incorporate the acetic acid extraction tech- 

 nique first introduced by Kamm et al.^^ for posterior pituitary hormones 

 and later developed by Payne et al.^^ for ACTH. In addition, oxycellulose 

 is employed to adsorb the MSH activity from the acetic acid extract accord- 

 ing to the procedure commonly used for the corticotropins. ^^ From these 

 MSH concentrates, highly purified or pure preparations may be obtained 

 with zone electrophoresis^^ or countercurrent distribution^^ or a combina- 

 tion of these two techniques. ^^•^''•^^•^^ 



Lee and Lerner^^ reported the presence in hog pituitary glands of two 

 substances possessing MSH activity; they observed two active peaks when 

 pituitary powder prepared from either posterior or anterior lobes was sub- 

 mitted to countercurrent distribution in a 2-butanol-0-5% aqueous tri- 

 chloroacetic acid system. The preparation with a high partition coeflScient 

 was designated as a-MSH, and the other component as j3-MSH. These 

 investigators beheve that a-MSH represents the main MSH component of 

 the hog pituitary gland because it accounts for the greatest percentage of 

 the total MSH activity. They ascribe the fact that other workers have ob- 

 tained jS-MSH as the main component to the step in the fractionation pro- 

 cedure of Landgrebe and Mitchell^^* involving precipitation with acetone, 

 during which they postulate that the a-MSH is separated from the jS-MSH 

 and discarded in the lyophilized filtrate. However, none of the other investi- 

 gators^^-^^-2°-^^ have detected the presence of a-MSH in the course of the 

 purification of their MSH preparations. 



The structure of the pig jS-MSH has been elucidated independently in 



* This explanation cannot be applied to the preparation of Geschwind and Li ;2i in 

 their procedure the supernatant fluid was lyophiHzed instead of being precipitated with 

 acetone. 



