Figure 6.

phLDH activity was measured in the presence of increasing concentration of polyclonal anti-phLDH antibodies (0 to 1000 nM or 0 to 156 μg/ml). phLDH activity (16 nM) was measured with free NADH (blue line), or in the presence of 240 μM rmGAPDH (red line) or 450 μM byGAPDH (green line). In all cases total NADH concentration was 40 μM, and the GAPDH concentrations are expressed in terms of NADH binding sites in each tetramer. Bulky anti-LDH antibodies can slightly inhibit the activity of phLDH with small NADH molecules and produce a significantly higher inhibition with the large GAPDH-NADH complex. The relative size of each molecule shows that bulky IgG molecules (PDB: 1IGT) can interfere with LDH-GAPDH interaction for all epitopes that are close to the NADH binding sites.