Glutathione reductase in wheat grain. 1. Isolation and characterization.

Durum wheat (Triticum durum, Desf.) endosperm of mature kernels contained a single form of glutathione reductase (GR); it appeared about the 18th day after anthesis while another isoform, present at the early stages of grain development, disappeared between the 20th and 30th days after flowering. The form that was present at grain maturity was isolated and characterized. It was composed of two monomers, each one having an apparent molecular mass of about 60 kDa. The K(m) values for NADPH and for GSSG were 3.7 and 9.1 microM, respectively, and the V(m) values for NADPH and for GSSG were 594 and 575 microkat.mg(-)(1) protein, respectively. The pH(i) of the enzyme was situated between pH 4.4 and 4.5. At a constant temperature of 25 degrees C, the optimum GR activity was found to be between pH 7.5 and 8.0. It was relatively resistant to high temperatures and was very resistant to very low temperatures.