We have described a case of Lactate dehydrogenase (LDH) linked to IgG (kappa) immunoglobulin which LDH isoenzyme pattern shows as if six bands are present. Of these bands, one additional is located at slow gamma region and such an anomalous appearance has not previously reported. The serum contains monoclonal immunoglobulin G (kappa) of which electrophoretic mobility is at slow gamma region (same as for abnormal LDH).
From reconstitution experiments, we concluded that all five LDH isoenzymes could bind to IgG prepared from the patient and those mobilities of the linked LDHs changed to cathodic side; LDH1, tailed to cathodic side; LDH2, moved to cathodic side; LDH3, located at slow LDH4; LDH4 located at fast LDH5; LDH5, located it slow gamma region; respectively. The affinity constant of each LDH isoenzyme was estimated and the values obtained from LDH1 to 5 were 0.026, 0.079, 0.166, 3.715, and 0.218. (Keg×109 liters/mol) was respectively. LDH4 evoked the highest affinity, it suggests that the site of antigen recognition of LDH linked to IgG was not associated with the structure of individual LDH-H and LDH-M subunits.
