Heterogeneity of human luteinizing hormone. Hydrophobic interaction chromatographic fractionation of some preparations.

The heterogeneity of human luteinizing hormone was investigated with high performance hydrophobic interaction chromatography on a TSK phenyl-5PW column using an ammonium sulphate gradient. Recovery of individual subunits, expressed as immunochemical activity, was in the order of 90%. Recovery of the intact hormone was less, approximately 25%. The technique appeared to be independent of the charge heterogeneity of the individual subunits. Each component as obtained by hydrophobic interaction chromatography showed considerable charge heterogeneity when studied by subsequent isoelectric focusing. Nonetheless, all chromatography fractions derived from either subunit showed the same collection of isoelectric values, quantitatively only differences for the beta-subunits could be detected. Heterogeneity of the individual subunits was clearly demonstrated after incubation of the preparations at 37 or 56 degrees C. The heterogeneity of the beta-subunit observed after incubation at 56 degrees C was different to the heterogeneity after incubation at 37 degrees C. After incubation at 56 degrees C, an additional component, with a longer retention time, developed directly from the intact molecule. The component is unstable and is transformed to one of the components detected also after incubation at 37 degrees C. Based on these results the existence of two populations of intact LH molecules with respect to their thermal stability is hypothesized.