Variability of Reaction Kinetics for Ribulose-1,5-bisphosphate Carboxylase in a Barley Population

The photosynthetic enzyme ribulose bisphosphate carboxylase-oxygenase [EC 4.1.1.39] (RuBPCase) plays a key role in the carbon reduction system of plants. In this study, we determined the kinetic variability of RuBPCase among 46 varieties of Hordeum vulgare L. at two ages. The V(max) CO(2) and K(m) CO(2) of RuBPCase was determined for each cultivar. Varietal differences were found in K(m) CO(2) and V(max) CO(2) for one and four genotypes, respectively. One variety exhibited atypical behavior in both K(m) and V(max). A comparison of varieties and age showed a significant interaction between these factors for K(m) but not for V(max). These data indicate the presence of kinetic variability in RuBPCase within the H. vulgare population and perhaps between plant ages.