Thermal Dependence of the Apparent Kmof Glutathione Reductase from Three Wetland Grasses and Maize

The thermal dependence of enzyme kinetic parameters has been presented as an indicator of species’ thermal optima and tolerance limits. Previous studies suggest the relationship between temperature and the apparent Michaelis–Menten constant ( Km ) of an enzyme system can be used to predict whole plant success at specific temperatures. The apparent Km for glutathione reductase (EC 1.6.4.2; GR) (oxidized glutathione as substrate) extracted from leaves of American sloughgrass ( Beckmannia syzigachne Steud.), tufted hairgrass ( Deschampsia caespitosa L.), tall fescue ( Festuca arundinaceae Schreb. ‘Titan’), and maize ( Zea mays L.), was determined over a range of temperatures (1–40 °C). For all species, minimum apparent Km for GR was observed at 1 °C, and Km values increased as temperature increased. The apparent Km values differed among all species at the lower temperatures (1–15 °C), but were similar at higher temperatures. The enzyme from tufted hairgrass had the lowest apparent Km at low temperatures (<15 °C), followed in increasing order by American sloughgrass, tall fescue and maize. Our experimental system failed to reproduce thermal kinetic window profiles similar to those reported elsewhere. With respect to the enzyme systems reported here, results suggest that these cool-season grasses can be ranked as more to less eurythermic within the temperature range from 1 to 15 °C. Copyright 0000