Biosynthesis, Processing, and Control of Release of Melanotropic Peptides in the Neurointermediate Lobe of Xenopus laevis

I N T R O D U C T I O N Several types o f melanot rop ic pept ides have been found in the pars in t e rmed ia o f lower ver tebra tes and m a m m a l s (Burgers , 1963; Preslock and Brinkley, 1970; Hopkins , 1972; Baker , 1973). T h e s e pept ides , including aand #-melanocy te s t imulat ing h o r m o n e (MSH), all contain a hep t apep t ide amino acid sequence, -Met -Glu-His -Phe-Arg-Trp-Gly, which appea r s to be the "active core" essential for melanot rop ic activity (i.e. to cause the expans ion o f melanocytes) (Eberle and Schwyzer, 1975). Adrenocor t i co t roph ic h o r m o n e (ACTH) and f l l ipotrophin (/3LPH) also are found in the pars in te rmedia , possess melanot rop ic activity, and contain this hep tapep t ide sequence. I ndeed , it has been p roposed that A C T H and ~ L P H are the p recursors o f orand /3-MSH, respectively, in the pars in te rmedia (Scott et al., 1973; Lowry and Scott, 1975; Bradbury et al., 1976). Al though the biosynthesis o f both A C T H and a M S H has recently been d e m o n strated in the rat neu ro in t e rmed ia t e lobe (Scott et al., 1976), systematic pulseTHE JOURNAL OF GENERAL PHYSIOLOGY " VOLUME 70, 1977 " p a g e s 3 7 5 8 3 7 on Jne 9, 2017 D ow nladed fom Published July 1, 1977