Growth hormone heterogeneity in American plaice pituitaries: Isolation, characterization, and partial amino acid sequence

Abstract

Growth hormones (GHs) have been isolated from pituitary glands of American plaice ( Hippoglossoides platessoides), a marine flatfish, using affinity and gel filtration chromatography, followed by preparative polyacrylamide gel electrophoresis (PAGE). A bioassay based on serum triiodothyronine elevation in immature rainbow trout was used to monitor biological activity. These GHs originate from two molecular mass regions, 42K and < 33K relative molecular mass ( M r), in their native state. The 42K M r region yielded two forms of GH, which differ in terms of quantity and net charge as evidenced by native PAGE, a major variant with a relative mobility of ( R f) 0.22 and a lesser variant with R f 0.28. The <33 M r region has a single GH species with R f 0.22. Upon sodium dodecyl sulfate-PAGE, without reduction, both GH variants from the 42K M r region gave M rs of 21K, while the GH from the <33K M r region was 20K M r, typical of monomeric vertebrate GHs. The proteins composing the 42K M r region are proposed as GH dimers since they yield 21K M r peptides. The <33K M r region contains a GH monomer (20K M r) in its native state. An aminoterminal amino acid sequence, identical for both the 42K and the 20K M r, R f 0.22 forms, has good homology with other complete fish GH sequences near their carboxyl-terminal regions (between amino acids 130 and 196). The GH dimers (42K M r) predominate in the plaice pituitary, contributing 93% of the total, of which 86% gives rise to the R f 0.22 variant.