Heterogeneity in electrophoretic mobility and in molecular size of lactate dehydrogenase-immunoglobulin G complexes

Some human sera have been found to contain lactate dehydrogenase (LDH)-immunoglobulin complexes. A serum with LDH-IgG3 complexes was further analysed. Complexes with different net charge and different molecular size were found. Their isoelectric points, measured by isoelectric focusing, were in the range of pH 6.3 to 7.2. Gel-filtration experiments showed that the molecular size varied from about 300 000 to 1 000 000. Most of the complexes could be precipitated from solution with 30--40% saturated ammonium sulfate or a low ionic strength.