Immunochemical Studies with Antisera to Fractions of Human Growth Hormone Which Are High or Low in Pigeon Crop Gland-Stimulating Activity1

Abstract

Chromatographically purified fractions of human growth hormone (HGH) which are relatively low in (A-peak HGH), or enriched in (B- and C-peak HGH), pigeon crop gland-stimulating (prolactin) activity were used as antigens to elicit antibody formation in the rabbit. Antisera to B-peak HGH, but not antisera to A-peak HGH, distinguished B- and C-peak from A-peak HGH by the immunochemical technique of quantitative micro-complement fixation. We infer from the immunological differences between A-peak HGH and B- and C-peak HGH that the 3-dimensional configurations of the 2 types of HGH are similar, but not identical, and that the antigenic differences between A-peak HGH and B-and C-peak HGH are due to relatively small, localized differences in configuration. The effects of reduction and carboxymethylation on the immunological activity of HGH were measured by complement fixation. Fully reduced and carboxymethylated HGH fixed less complement than untreated HGH with anti-HGH. The decrease in immunological activity was greater when measured with anti-B-peak HGH than when measured with anti-A-peak HGH. Immunological relatedness between a protein of human placental origin (human placental lactogen) and HGH was measured by complement fixation. The placental protein fixed complement with anti-A-peak HGH and anti-B-peak HGH, but the cross-reactions required 6 times more antiserum than was needed to detect the homologous reaction with HGH. Reciprocal cross-reactions between HGH and antiplacental protein were performed. In the region of antibody excess, C-peak HGH fixed more complement than A-peak HGH with antiplacental protein.