Immunochemical Homologies among Vertebrate Lactate‐Dehydrogenase Isozymes

Lactate dehydrogenase A4, from possum, chicken, and sardine muscle extracts and lactate dehydrogenase B4, from chicken heart and sardine muscle extracts have been purified. Specific activity determinations confirmed previous studies showing the A4, isoenzyme to be approximately twice as efficient as the B4, isozyme and fish lactate dehydrogenase A4, to be considerably more active than the corresponding enzyme in warm‐blooded animals. Spectrophotometric analyses demonstrated striking similarities in ɛ2801 mg/ml values, which reflected a uniform tryptophan content (5 residues lactate dehydrogenase subunit) in the enzymes analysed. Sheep antisera were prepared against each isoenzyme and used in immunochemical titration experiments to measure the extent of inhibition, precipitation and interaction of the lactate dehydrogenase isozymes by the antisera. Lactate dehydrogenase antibodies differed in their immunochemical specificities according to the nature and source of the antigen. For example, the relative affinities of antiserum to possum A4, isozyme for the enzymes was in the order, possum A4 >, chicken A4 > sardine A4, ≫, sardine B4 >, chicken B4, which compared with the affinities for antichicken B4, chicken B4 >, sardine B4≫ sardine, chicken and possum A4. In contrast to the results of other workers, isozymes A4, and B4, were shown to be immunochemically related. This observation is attributed to the higher degree of sensitivity in recognizing enzyme‐antibody interactions using gel zymogram/immunochemical technique. The antisera were also used in investigating the immunochemical properties of isozymes A′4, A′4, B4, B′4, and E4, from trout, and isozymes A4, B4 and C4 from pigeon, kangaroo and rat‐tissue extracts. These vertebrate lactate dehydrogenase isozymes shared common antigenic determinants which reflected differing degrees of sequence homology and a common evolutionary origin.