A 36,000-Mr protein purified from mouse myeloma on the basis of selective binding to a single-stranded DNA (ssDNA)-cellulose column has been identified as the lactate dehydrogenase A (LDH-A) subunit. A homogeneous preparation of this mouse myeloma ssDNA-binding protein, termed the ‘low-salt-eluting protein’, was found to possess LDH activity, and rabbit antiserum prepared against this protein was shown to cross-react with purified 36,000-Mr LDH-A subunits from mouse and bovine sources. In addition, bovine and human LHD-A4 isoenzymes were shown to be capable of binding ssDNA. These enzymic and immunological identities with LDH-A were not observed with purified helix-destabilizing protein 1 from mouse myeloma. A model for ssDNA-LDH binding is discussed.

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