Immunochemical Homologies among Vertebrate Lactate‐Dehydrogenase Isozymes

Abstract

Lactate dehydrogenase A 4 , from possum, chicken, and sardine muscle extracts and lactate dehydrogenase B 4 , from chicken heart and sardine muscle extracts have been purified. Specific activity determinations confirmed previous studies showing the A 4 , isoenzyme to be approximately twice as efficient as the B 4 , isozyme and fish lactate dehydrogenase A 4 , to be considerably more active than the corresponding enzyme in warm‐blooded animals. Spectrophotometric analyses demonstrated striking similarities in ɛ 280 1 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 A 4 , isozyme for the enzymes was in the order, possum A 4 >, chicken A 4 > sardine A 4 , ≫, sardine B 4 >, chicken B 4 , which compared with the affinities for antichicken B 4 , chicken B 4 >, sardine B 4 ≫ sardine, chicken and possum A 4 . In contrast to the results of other workers, isozymes A 4 , and B 4 , 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 , B 4 , B′ 4 , and E 4 , from trout, and isozymes A 4 , B 4 and C 4 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.