COMPARATIVE-STUDIES ON THE SOLUBLE AND PLASMA-MEMBRANE ASSOCIATED NITRATE REDUCTASE FROM CUCUMIS-SATIVUS L

The biochemical comparison between two forms of nitrate reductase from cucumber roots: the soluble enzyme and the plasma membrane-associated one was made. Soluble nitrate reductase was purified on the blue-Seph arose 4B. The nitrate reductase bound with plasma membranes was isolat ed from cucumber roots by partition of microsomes in the 6.5% dextran- PEG two phase system. The molecular weight of native enzyme estimated with HPLC was 240 kDa and 114 kDa for the soluble and membrane bounded enzyme, respectively. Temperature induced phase separation in Triton X-114 indicated a huge difference in hydrophobicity of the plasma memb rane associated nitrate reductase and soluble form of enzyme. Small di fferences were observed in partial activities of plasma membrane nitra te reductase and soluble nitrate reductase. Also experiments with poly clonal antiserum raised against the native nitrate reductase showed so me differences in the immunological properties of both forms of the ni trate reductase. The above results indicated that in cucumber roots tw o different forms of the nitrate reductase are present.