Molecular forms and thermal and kinetic properties of purified glutathionereductase from two populations of barnyard grass (Echinochloa crus-galli (L.) Beauv.: Poaceae) from contrasting climatic regions in North America

The thermal, kinetic, and electrophoretic properties of purified glutathion e reductase (GR; EC 1.6.4.2) were analyzed in plants from two ecotypes of b arnyard grass (Echinochloa crus-galli (L.) Beauv.: Poaceae) originating fro m sites of contrasting climates in Quebec (QUE) and Mississippi (MISS). Cru de and purified GR preparations from plants of both ecotypes consisted of o ne homodimer isomorph with the same electrophoretic mobility in polyacrylam ide gels, a similar molecular mass for the native enzyme (98 kDa) and for e ach subunit of the dimer (44 kDa), and an identical pI of 5.9. The electrop horetic profile of GR purified from cold-acclimated plants at 14 degrees C light (L) : 8 degrees C dark (D) for 10 days was similar to that of GR from plants grown at 26 degrees C L : 20 degrees C D. Specific activities of pu rified GR from QUE plants were significantly higher than those of MISS plan ts. In vitro GR activities from QUE and MISS plants were not differentially affected by thermodenaturation at 55 or 65 degrees C or by cold treatments at 2 degrees C. Apparent energies of activation (E-a) of GR purified from QUE and MISS plants were similar with the exception of estimates of E-a (ox idized glutathione) for Q(10) (15-5 degrees C) for which significantly lowe r values were obtained for QUE plants. No differences of physiological sign ificance were observed for K-m (Michaelis-Menten constant) values of GR pur ified from QUE and MISS plants. However, both V-max and K-cat (turnover num bers) estimates were significantly higher for GR purified from QUE plants o ver most of the range of assay temperatures, suggesting superior catalytic efficiency for the enzyme of the cold-adapted ecotype from Quebec.