The Segment Assay of the Adrenocorticotrophic Hormone
Until recently ACTH was regarded as a single, well-defined polypeptide of 39 amino acids. The structure of ACTH derived from the pituitary gland of several species, its physical chemistry and possible three-dimensional structure and conformational changes, have been reviewed by Schwyzer (1977; also see Ney et al. 1964). However, as shown by Orth and Nicholson (1977) it now seems to be only a ‘central element in a wide array of biosynthetically-related polypeptides’. The potential precursor of all these hormones may be big ACTH (Rees 1977) or very big ACTH (Orth and Nicholson 1977) so that the lipotrophins (the large β h -LPH and the γ h -LPH), ACTH, the endorphins, α- and β-MSH, and the ACTH-like intermediate lobe peptide (CLIP) are all related. Thus α-enkephalin corresponds to β-LPH61–65; β-endorphin to β-LPH61–91; β-MSH which, in the human but not in other species, now seems to be an extraction artefact (Rees, 1977) corresponds to β-LPH41–58 while α-MSH is equivalent to N-α-acetyl [ACTH1–13]-NH2; and CLIP is ACTH18–39 (Orth and Nicholson 1977; Rees 1977). The possible relationships have been discussed by Smyth (1978) and are shown in Fig. 7.1.
KeywordsCholesterol Polypeptide Trypsin Glucocorticoid Progesterone
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