Immunochemical study of immunoglobulins bound to lactate dehydrogenase.

Immunochemical analysis of lambda type Bence Jones protein (BJP: designated as Suzuki-BJP) and IgG-lambda type M-protein (designated as Miki-IgG), lambda type BJP (designated as Miki-BJP) which showed non-specific binding with lactate dehydrogenase (LD, EC 1.1.1.27) was carried out in two cases. When the purified LD mixed with NADH was eluted through the CNBr-Sepharose 4B coupled to Suzuki-BJP or Miki-IgG, the affinity with these adsorbents was not demonstrated. The amino acid residue of the N-terminal in the Suzuki-BJP and lambda chain of the Miki-IgG was determined to be tyrosine by primary structure analysis, on the other hand, alanine was detected in the gamma chain of the Miki-IgG that did not have LD binding ability. By counter affinity electrophoresis, it was shown that LD bound to a synthetic peptide consisting of 15 amino acid residues of N-terminal which had the same beta-sheet structure as the Suzuki-BJP. It seems probable that LD combines with BJP (or IgG) molecule at the NAD+ binding site producing a three-dimensional structure similar to NAD+.