Luteinizing Hormone. 1. Circular Dichroism and Spectrophotometric Titration of Porcine and Bovine Hormones and of Their alpha and beta Subunits

Spectrophotometric titrations of porcine and bovine luteinizing hormones and of their subunits have been performed. Despite specific differences in primary structure, similar results were obtained for both hormones as well as for each of their two subunits. While only five out of seven phenolic hydroxyl groups of tyrosyl residues were ionized in the native hormones at alkaline pH, all were titrated in the isolated subunits. From circular dichroism spectra and spectrophotometric titration data it can be assumed that two tyrosyl residues, buried in the native hormones, are exposed to the solvent medium in the isolated subunits.