Activation and inhibition of human alcohol dehydrogenase by monoclonal antibodies

The human class I alcohol dehydrogenase isozyme β 2 β 2 was used as the antigen to raise monoclonal antibodies. Altogether seven lines of hybridomas secreting monoclonal antibodies were obtained. None of the antibodies was isozyme specific and all of them exhibited a similar affinity against all isozymes of the human class I ADH. Five out of the seven monoclonal antibodies had no effect on β 2 β 2 activity. Antibody G3 acted as a non-competitive inhibitor with a K 1 of 3 μg/ml at pH 7.5. Increasing pH was effective in reducing the level of inhibition. On the other hand, antibody 1D4 exhibited a pH-dependent activation of ADH activity. In the presence of this antibody, the pH optimum of β 2 β 2 was shifted from 9 to 8.5 and total activity was increased by 70% at this optimal pH. Kinetic analysis indicates that 1D4 probably acts as a non-competitive activator and may exert its actions by interacting with the coenzyme binding site.