Abstract
SM-A isolated from human plasma is a neutral polypeptide MW 7000, with an anabolic effect in vitro. Determination by specific radioligand assay in serum samples shows a positive correlation to growth hormone status. SM-A is present in serum bound non-covalently to carrier proteins. When sera from normal individuals and acromegalic patients is gel-filtered at neutral pH on Sephadex G-200 SM-A activity is found in the region MW 100,000 (Form I) and 70,000 (Form II). Untreated hypopituitary patients lack the Form I, but apparently this is formed upon GH treatment. The carrier proteins have been purified from plasma by PEG precipitation, ion-exchange chromatography and gel-filtration. Form I differs from Form II both by size and charge and is a glycoprotein. SM-A can be dissociated by acid pH from the carrier protein into the low MW form. A third form of high molecular weight somatomedin, not dissociable in acid is also found in plasma. This corroborates with the findings of Poffenbarger and co-workers.
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Fryklund, L., Hall, K., Enberg, G. et al. Somatomedin (SM-A) and the carrier proteins: regulation by growth hormone. Pediatr Res 12, 1087 (1978). https://doi.org/10.1203/00006450-197811000-00035
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DOI: https://doi.org/10.1203/00006450-197811000-00035
