Immunochemical characterization and quantification of larval brine shrimp malate dehydrogenase

The cytosolic malate dehydrogenase (s-MDH) from larval brine shrimp has been immunochemically characterized by quantitative rocket immunoelectrophoresis (IEP) and antibody catalytic inhibition studies. Monospecific rabbit antiserum produced against purified naupliar s-MDH was used for rocket IEP as a quantitative assay for the cytoplasmic isozyme, Since cross-reactivity was not observed against the mitochondrial MDH (m-MDH), the assay allows specific measurement of the s-MDH in crude naupliar supernatants in the presence of contaminating m-MDH. The assay has a sensitivity of approximately 100 nanograms s-MDH protein using either purified enzyme solutions or crude supernatant preparations. Catalytic inhibition studies using the monospecific antiserum gave 85% inhibition of s-MDH but did not give significant inhibition of the m-MDH. Lack of complete s-MDH inhibition by the antiserum suggests a difference between the enzyme active site and immunological binding site. Although the antiserum was produced against s-MDH from nauplii of the San Francisco Bay population, the antiserum inhibits equally well the s-MDH of Great Salt Lake (Utah) nauplii, indicating little if any structural difference in the immunological sites of the s-MDHs from these two geographical sources. Porcine (s- and m-MDH), bovine (m-MDH), and pigeon (m-MDH) were also tried as antigens against the brine shrimp s-MDH antiserum, but antigen-antibody reactivity was not observed during rocket IEP or catalytic inhibition experiments.