Detection of glycosylated growth hormone-binding proteins in rat serum

Affinity cross-linking technique revealed the presence of three growth hormone-binding proteins (GHBP) in dealbuminized rat serum. The apparent molecular weights, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, were 52,000, 44,000 and 39,000. By use of carbohydrate chain cleaving enzymes it was found that the binding proteins contain N-linked complex carbohydrate chains, representing 8000, 4000 and 5000 in apparent molecular weight, respectively. Gel permeation chromatography and sucrose density gradient centrifugation revealed a growth hormone-binding entity with Stoke's radius 94.5 A (+/- 2.8, n = 5) and an s-value of 10.8 S (+/- 0.31, n = 5). The molecular weight could be calculated to 413,000. Both for gel chromatography and sucrose density gradient experiments unlabelled growth hormone reduced the radioactive peaks from 0 to 50%. The relation of this binding entity to the GHBP's described with affinity cross-linking technique and the nature of this binding entity is at present unclear. No serum binding protein(s) for prolactin was detected by affinity cross-linking technique, gel permeation chromatography or sucrose density gradient analysis.