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

The charge heterogeneity of an LH preparation containing relatively acidic components (LH Type I) 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 α-subunits, with pI-values of 4.49, 4.79, 5.16 and 6.02 could be detected after incubation at 37°C. With the exception of the most acidic component all these α-subunits were also present in earlier studied LH 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 LH Type II preparations. The β-subunits detected were very different from those observed in Type II preparations. All six components detected had pI-values < 7.5. Upon incubation at 56°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 β-subunits observed before in Type II preparations. After neuraminidase treatment, the pH values of the population of β-subunits became identical to those of the population in LH Type II. From these results it is concluded that the major charge difference between LH Type I and Type II is located in the β-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.