Characterization of putative growth hormone receptors in human choroid plexus

The ability to bind iodine-labelled human growth hormone ([125I]hGH) was measured in different parts of the human brain. The choroid plexus contained the highest amount of binding sites (receptors) and was therefore selected for further studies. The binding between [125I]hGH and the receptor was saturable, of high affinity (Ka = 0.63 nM-1) and pH- as well as time-dependent. After solubilization with Triton X-100 the receptors retained their hormone-binding properties and eluted in the high molecular weight range (greater than 500,000) upon molecular sieve chromatography. Analysis by an affinity cross-linking technique indicated a hormone-binding unit of molecular weight 51,000. The molecular characteristics of the identified binding sites are discussed in comparison to those of growth hormone receptors of human and animal origin.