The mechanism and analysis of abnormal immunoglobulins that inhibits lactate dehydrogenase activity

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We review the characterization of lactate dehydrogenase (LD)-immunoglobulins complex and the mechanism of LD inhibition by abnormal immunoglobulin. In Bence Jones protein (BJP) which combines with LD, it has been considered that LD binds the abnormal immunoglobulin which has an aromatic amino acid at the first portion of N-terminal, such as tyrosine and abnormal three-dimensional structure, such as longer β-sheet structure of N-terminal. However, the mechanism that is responsible for formation of immunoglobulins with LD inhibition is unclear. We recently discovered a patient with low LD activity and an abnormal LD isozyme pattern. The LD activity of the patient's serum was inhibited more strongly at 4° than at 37°. The immunoglobulin responsible for LD inhibition was an IgAl- λ. The LD inhibition by the patient's IgAl was blocked by reduction and alkylation and by NADH. Polymerization of the patient's IgAl might play an important role in its interaction with LD. Moreover, the possibility exists that part of the patient's IgAl gets into a pocket of LD in the absence of NADH, and that LD recognizes the patient's IgAl at the NAD<SUP>+</SUP>-binding site of LD, since that part of the patient's IgAl may appear similar in structure to NAD<SUP>+</SUP>.