Abstract
Several types of modifications of serum lactic dehydrogenase (LDH) isoenzymes were previously reported, such as modifications due to complex formation with immunoglobulins, binding of NAD, and existence of an inhibitory factor to LDH-H subunit. This report is presenting two types of new modifications of LDH isoenzymes.
The first case concerned a 69 year-old male with rectal carcinoma and impending myocardial infarction. Serum LDH activity was within the normal limits and the enzymogram on Cellogel showed the normal electrophoretic mobilities except that LDH-III was broadened. and skewed to the cathode. On Sephadex G-200 gel filtration (0.02 M phosphate buffer pH 7.4, or Veronal buffer pH 8.6μ=0.06), the LDH activities were detected only between G and M fractions (M. W. 21×104), but not between A and G where LDH of the normal molecular size was expected to elute. On the other hand, under the condition of a higher ionic strength (0.02M phosphate buffer +0.5M NaCl pH 7.4), the enzyme activities disappeared in an abnormal position and newly appeared between A and G (11×104). These findings suggest that all of LDH in this case form high molecules and dissociate under a high ionic strength. The patient's serum was observed to convert LDH of normal size of the other serum into high molecules. Some component other than the enzyme was suspected to be responsible for formation of the macro-molecular LDH. However, by the method of immunoelectrophoresis followed by activity staining, LDH activities were not detected on the all of the precipitin lines by using anti-human whole serum or anti-immunoglobulins serum. This fact and the mild condition for dissociation may suggest that some proteins other than immunoglobulins would be involved in formation of the macro-molecular LDH. Both of the separated fractions of an abnormal and normal molecular size gave the same electrophoretic pattern and the same mobility. This case was thought to be a new type of macro-molecular LDH with such properties as normal electrophoretic mobility and the mild condition for dissociation.
The second type of LDH modifications was revealed in the survey of patients with a low activity of serum LDH-V which was considered to be not corresponding to elevation of GPT. One of these cases concerned a 61 year-old male with cardiac failure. Serum LDH activity was 100 W. U. and only LDH-I was electrophoretically observed with the traces of other isoenzymes. But hemolysate of the same patient was normal in isoenzyme pattern. The patient's serum was observed to inhibit an isoenzymes containing M-subunit of the other serum. Another case was a 69 year-old male with cardiac failure, whose serum was also inhibitable to M-subunit of the other serum. After dialysis of serum with a high LDH-V activity against this patient's serum, the isoenzymes containing M-subunit of the former were strongly inhibited. When the patient's serum was dialysed against 0.02 M Tris buffer, the ability of inhibition was completely lost. This ability was preserved under the condition of 80°C for 15 min.
The first type of LDH anomaly was estimated as a modification, either due to homo-dimer formation of LDH isoenzyme molecules with some binding factor of a small molecular size, or to complex formation with some protein which is of the molecular weight of about 10×104 and has no contribution to the electrophoretic mobility of LDH.
The second type was proved to be a modification due to existence of M-subunit inhibitor which is dialyzable and heat stable.
These modifications may offer new problems to interpretation and clinical application of serum LDH isoenzymes.
