The growth hOrmone-prolactin family

Growth hormone (somatotropin GH) is a protein hormone produced in specific cells (somatotrophs) of the pituitary gland. It comprises a single polypeptide chain of about 190 amino acids which folds, with formation of two disulphide bridges, to a compact tertiary structure (see also Addendum, p. 289). Amino acid sequences have been determined for GHs from several species [1,2] and these reveal a considerable amount of species variation in particular, human GH shows extensive differences from the GHs of non-primate mammals, and this has been interpreted as indicating a rapid rate of evolution for the GH gene in the primates [3,4], Differences in biological properties between human and non-primate GHs have also been observed, and will be considered later. 

Other members of the GH-prolactin family include the placental lactogens and a prolactin-like protein, proliferin. A placental lactogen is produced in large amounts 

Another recently discovered member of the GH-prolactin family is the prolactinlike protein proliferin. This was first shown to to produced by actively proliferating (but not quiescent) mouse fibroblasts [13] but is now known to be present also in the mouse placenta, although it is distinct from the mouse placental lactogens. 

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