The present invention relates to somatotropin analogues with amino acid changes in the alpha -helix 3 regions of said somatotropins, changes in the alpha -helix 2 regions, combinations thereof plus combinations with other changes to the native amino acid sequence of somatotropins. The resulting analogues are stable for formulation in sustained release formulations, while maintaining biological activity. Further, methods for conducting site-directed mutagenesis on DNA encoding proteins and/or polypeptides also are provided.
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