AbstractThe response of the kinetic properties of NAD malate dehydrogenase (MDH) was compared for two clones ofLathy rus japonicusWilld. collected in two contrasting climatic sites in Eastern North America. MDH from the cold adapted maritime genotype (Hudson Bay, Québec) had lower thermostability, reduced apparent (Ea) and free (ΔG†) energy of activation and lower specific activity when compared to MDH of plants from the warm summer continental site (Lake Michigan). Electrophoretic analyses show little differentiation in the isozyme profiles of the two genotypes. Thermostability differences were primarily associated with the mitochondrial isozymes which, however, were not differentiated electrophoretically Substrate binding ability of MDH, as measured by apparent Km, was more sensitive to high assay temperature in the cold adapted maritime genot