HIGH-MOLECULAR-WEIGHT GROWTH-HORMONE (GREATER-THAN-160 KD) IN HUMAN SERUM CHARACTERIZED WITH MONOCLONAL-ANTIBODIES

Human growth hormone (hGH) was analyzed by six monoclonal antibodies ( Mabs) and a polyclonal antiserum (Pas) before and after molecular siev e chromatography of sera from healthy subjects. Their hGH levels were between <0.2 and 0.4 ng/ml as determined with Pas. The six Mabs reacte d with five distinct epitopes and bound to a hGH fragment correspondin g to the amino acid sequence 15-125. Two of the Mabs showed reduced bi nding to 20-kD hGH. The binding of Mabs to dimeric forms of hGH varied . Human GH levels in unfractionated sera as determined with Mabs were <3.1-390 ng/ml. After molecular sieve chromatography of the sera, one peak of hGH-immunoreactive material of high molecular weight (>160 kD) and one at the elution volume of monomeric hGH were determined with P as and Mabs. The major part of the high molecular weight hGH (> 160 kD ) seemed to consist of 22-kD hGH molecules, since Pas and all Mabs det ected the hGH immunoreactivity (>160 kD) in a similar manner. This hig h molecular weight hGH (>160 M)) was distinguishable from the identifi ed, receptor-like hGH-binding protein in serum.