Molecular forms and kinetic properties of the mitochondrial fraction of NAD-malate dehydrogenase in four clones of Lathyrus japonicus (Leguminosae) from sites of contrasting climates

Abstract

The molecular forms and kinetic properties of the mitochondrial fraction of NAD-malate dehydrogenase (mt-MDH) were analyzed in four clonal populations of Lathyrus japonicus collected from sites of contrasting climates in eastern North America and acclimated to three experimental thermoperiods. Three molecular forms of mt-MDH were separated in eight different starch and acrylamide electrophoretic systems, and isoelectric focusing (IEF) disclosed nine isozymes with isoelectric points in the 6.7–8.2 pH range. No differences in the electrophoretic or isoelectric focusing patterns were observed between clones acclimated to any of the three thermoperiods. Apparent Km values and Vmax/Km ratios for oxalacetate were obtained at 14 assay temperatures ranging from 2.5 to 35 °C. Km values were lower in the 10–20 °C range and increased markedly at higher and, particularly, at assay temperatures below 10 °C. Acclimation had a marked effect upon Km values obtained at extreme assay temperatures. Km values were significantly higher for assays in the range of 30–35 °C for plants of the two cold-adapted clones grown at 7–15 °C and 15–25 °C. Vmax/Km ratios were lower over the 30–35 °C segment of the assay curve for mt-MDH of the two cold-adapted clones acclimated at 7–15 °C and 15–25 °C and acclimation modified the shape of the curves of Vmax/Km ratios for mt-MDH from the four clones. Results suggest that modifications in kinetic behaviour of mt-MDH among Lathyrus japonicus clones represent adjustments for the modulation of catalysis in response to temperature conditions at the original sites of collection of the clones.