Heterogeneity of human luteinizing hormone. Discrimination between acidic and basic preparations

The charge heterogeneity of an I. H preparation containing relatively acidic components (LH Type 1) was studied. Four biological active components, with pI-values of 5.04, 5.60, 6.06 and 6.57 were detected. A total of four different alpha-subunits, with pI-values of 4.49, 4.79, 5.16 and 6.02 could be detected after incubation at 37 degrees C. With the exception of the most acidic component all these alpha-subunits were also present in earlier studied 1.H Type II preparations. After neuraminidase treatment a strong shift to more basic components was observed, resulting in a population of components similar to the one detected in I.H Type II preparations. The beta-subunits detected were very different from those observed in Type II preparations. All six components detected had pI-values greater than 7.5. Upon incubation at 56 degrees C these subunits appeared to be unstable resulting in a shift to more basic pI-values these pI-values being very similar to those of beta-subunits observed before in Type II preparations. After neuraminidase treatment, the pH values of the population of beta-subunits became identical to those of the population in I.H Type II. From these results it is concluded that the major charge difference between LH Type I and Type II is located in the beta-subunits. This difference cannot be explained completely by differences in sialic acid content, but may also be due to heat labile charged groups such as sulphate.