A preparation of human pituitary somatotropin examined in quantitative polyacrylamide gel electrophoresis is conformationally compact. The derived molecular weight by quantitative electrophoresis is consistent with the known mass of the hormone and values obtained by other methods. A plasmin modified somatotropin is more compact and shows full activity in immunoassay, and in lymphocyte binding and somatotropic assays, with enhanced lactogenic activity. The N terminal 134 amino acid fragment and a hendekakaihekaton fragment exist in non monometric forms. The N terminal fragment has immunologic and biologic activity, with greatest activity in the in vivo somatotropic assay. The hendekakaihekaton fragment exhibited only marginal activity. All preparations showed heterogeneity of charge in quantitative electrophoresis with discrete charge isomerism recognizable for the native and plasmin modified preparations.
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