Abstract
The molecular weight of bovine heart supernatant malic dehydrogenase has been determined by sedimentation equilibrium. The enzyme was shown to be a dimer with a molecular weight of 72,000. Upon reaction with maleic anhydride or in the presence of guanidinium chloride, the enzyme was dissociated into two subunits having identical molecular weights of about 37,000 as determined by sedimentation equilibrium. These results were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and peptide mapping experiments. The COOH-terminal amino acid residue of both subunits was identified as alanine, and cleavage by carboxypeptidase digestion did not affect the catalytic activity of the enzyme. Circular dichroism measurements showed that the dissociation of the enzyme by maleic anhydride and guanidinium chloride was accompanied by significant amounts of unfolding in the protein.
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