Abstract
The complete amino acid sequences of two variants of cod growth hormone (GH) have been determined. The GHs, which have apparent molecular weights of 20K and 22K in SDS-PAGE, consist of 185 amino acids and have calculated molecular weights of 20,733 and 20,805, respectively. Comparison of the two sequences showed only one amino acid difference between the variants, with Lys at position 151 in the 22K GH changed to Gly in the 20K GH. The substitution of a charged amino acid by one which contains no sidechain might be expected to be reflected in the isoelectric point of the molecule. However, the observed pI for both the 20K and 22K GHs was 5.8. The difference in apparent molecular weights by SDS-PAGE suggests the existence of a conformational difference between the variants which is attributable to the observed substitution. This conclusion is in agreement with our previous data obtained from radioimmunoassay studies where the 20K GH shows only 25% cross-reactivity in an assay developed for the 22K GH. Alignment of the cod GH sequence with those of other teleost GHs reveals cod GH to be most similar to advanced marine fish such as tuna, sea bream, bonito, and yellowtail (76-83% identity), whereas it is 62-66% identical to flounder and chum salmon GH.
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