Abstract
Highly purified growth hormone (GH) has been prepared from the pituitary glands of a euryhaline teleost, Tilapia mosambica. Tilapia GH was obtained in a yield of 1400 mg/kg wet weight tissue. It was found to have a molecular weight (gel filtration) of 22,200 daltons, a sedimentation coefficient ( s 20,w) of 2.19, and an α-helix content (circular dichroism) of 50%. Isoleucine was found to be the major amino-terminal residue; leucine was found to be COOH terminal. The amino acid composition, disc gel electrophoresis pattern, and circular dichroism spectra were similar to those of mammalian GHs. Tilapia GH was found to have a low but significant activity in the rat tibia assay and showed immunological relatedness to mammalian GH in a rat GH radioimmunoassay. Antiserum was prepared against the Tilapia GH and characterized in agar diffusion experiments and radioimmunoassay. Results from these investigations demonstrated a significant degree of cross-reaction between Tilapia GH and pituitary extract from another teleost (perch), but purified tetrapod GHs were essentially nonreactive. The data indicate a significant resemblance between Tilapia GH and mammalian GHs and suggest that the GH structure has been strongly conserved during evolution.
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