Heterogeneity of human lutropin. Detection and identification of α- and β-subunits

A highly purified LH preparation, prepared from human pituitaries (NM14) was studied using immunochemical and in vitro biological techniques. Using isoelectric focusing 5 different biologically active components could be detected, 4 of which were located between pH = 7.0 and 8.6, one was located at pH = 4.9. The biological activity in the acidic part of the pH gradient is probably due to the formation of an artefact during storage in solution. The experiments were performed with special emphasis on the occurrence of LH subunits, for which until now no pI-values have been reported. Using specific radioimmunochemical (RIA) systems at least 7 different α-subunit components and 4 different β-subunit components could be detected. The presence of even more components is likely. The α-subunit components, with pI-values of: 4.6, 5.2, 6.0, 7.1, 8.1, 8.8 and 9.7, were located spread over the entire pH-gradient whereas all β-subunit components were located above pH = 7.5, the pI-values being 7.7, 8.4, 8.5 and 10.4. The identification of these components as α- or β-subunit was based on the relative response in the different RIA systems, the absence of biological activity and the response changes during incubation at 37°C. Refocusing of the above mentioned biologically active components individually resulted each time in a single component with a pI-value identical to its corresponding 'parent'. After incubation at 37°C of these components each time the same variety of subunit components was found with discrete pI-values, identical to those above.