Primary structure of alpaca growth hormone

Reduced and carbamidomethylated alpaca growth hormone was submitted to tryptic digestion. Peptides in the mixture were purified by reverse phase HPLC and N-terminal determination and an amino acid analysis of each was performed. Data obtained and the already known primary structure of the equine growth hormone allowed the assembly-by homology-of a definite sequence of amino acids for the polypeptide chain of the protein. Present data provide further information about the relationship between growth factors.     

ISOLATION AND CHARACTERIZATION OF ALPACA GROWTH HORMONE

A simple and mild procedure is described for the isolation of pituitary growth hormone from alpaca glands. It involves extractions in buffer at pH 8. 7 and gel filtration in Sephadex G-75. An average yield of 1 mg purified product may be obtained from 1 g fresh alpaca pituitary glands. The alpaca hormone was exam ined for homogeneity by SDS-polyacrylamide gel electrophoresis, gel electro-focusing and end-group analyses. It is a protein composed of a single polypeptide chain with phenylalanine at both ends. The C-terminal sequence is -Ala-Phe. The molecular weight is approximately 21700 and the amino acid composition very similar to that observed in equine growth hormone.     

TRINITROPHENYLATION OF BOVINE GROWTH HORMONE

Bovine growth hormone was chemically modified with picryl sulfonic acid, at pH 8.4 during 2 and 5 min of reaction. The N-terminal residue provides the most reactive amino group followed by the amino groups of lysine 179 and lysines 143, 69, 111, 170 and 166 in decreasing order. These results agree with those obtained previously with equine growth hormone, except that residue 156 is not modified in bovine growth hormone, An important decrease in biological activity occurs between 2 and 5 min of reaction without sensible modification in the α-helix content of the molecule.     

Ethoxyformylation of histidine residues in equine growth hormone

Reactivity of histidine residues in equine growth hormone to ethoxyformic anhydride was studied. The existence of two kinetically different sets was demonstrated: one of them including only the slow reacting histidine 169 (k = 0.164min^-1) and the other containing fast reacting histidines 19 and 21 (k = 0.892 min^-1). A correlation between the decrease in the capacity to compete with ¹²⁵I-labeled hormone for rat liver binding sites and the degree of ethoxyformylation of the fast group was found. Circular dichroism studies indicated no significant conformational changes in the protein with all three residues modified. These results fully agree with those obtained for bovine growth hormone which is further evidence supporting the vinculation of histidines 19 and/or 21 with the binding site of these hormones to their specific receptors.     

An equine growth hormone molecular species lacking the 76-92 peptidic fragment

A new eGH molecular species was isolated and purified by reverse phase HPLC. SDS-polyacrylamide gel electrophoresis, amino acid composition, and C- and N-terminal determinations support a primary structure identical to that described by Zakin el al. (1976), except for the lack of the 76-92 peptidic fragment and the maintaining of 30% of its biological activity.