A screening method for measuring somatomedin B protein binding in serum from children with growth retardation

A simple method which uses 100 microliter serum has been developed to measure the binding of somatomedin B (SMB) to protein in serum from normal children, adults, and patients with growth hormone deficiency. 125I-labelled SMB was used as binding ligand. The correlation between the binding of label by the proposed procedure and by an immunoelectrophoretic technique was acceptable (r = 0.73; P less than 0.02). The mean percentage of label bound to protein in serum from patients with deficiencies of growth hormone or other trophic hormones was significantly (P less than 0.001) lower than that for controls. The physicochemical characteristics of a specific binding-protein suggested that a protein with low capacity (160 pmol/l) and low Ka (4.37 X 10(6) l/mol was present in serum, in addition to a high concentration of alpha globulin(s) which also bound 125I SMB.