Characterization of human LH isohormones from fresh pituitary tissue

The pattern of human LH (hLH) microheterogeneity was determined using freshly obtained pituitary tissue. Chromatofocusing across a pH 9-6 gradient produced several, distinct peaks of hLH immunoreactivity between pH 8.5 and 6.8, as well as a 'salt peak'. Chromatofocusing of the 'salt peak' across a pH 7-4 gradient yielded distinct peaks of hLH at pH 6.1, 5.6, and 5.4. Pituitary tissue obtained at surgery produced a virtually identical pattern. By gel filtration the elution volume of each major chromatofocusing peak was similar to that of intact hLH, rather than those of the hLH subunits. The bioactivity/immunoreactivity ratios of the major chromatofocusing peaks fell dramatically with decreasing pH, from approximately 8 at pH 8.5 to approximately 1 at pH less than 6. These results indicate that human pituitary LH exists in multiple, isomeric forms that differ markedly in charge and bioactivity. These differences appear to be inherent in the native, intact molecules and not the result of autolysis or of dissociation into subunits.