An improved equation and assay for determining the CO(2)/O(2) specificity for Rubisco.

The determination of the CO(2)/O(2) specificity factor (Omega) is very important to investigate the Rubisco carbon assimilation efficiency. In this paper, it is proved that previous formulae can introduce notable errors into calculating the CO(2)/O(2) specificity factor (Omega) because CO(2) and O(2) are both the substrates and the mutually competitive inhibitors for Rubisco. A simple integrated equation is proposed to calculate the CO(2)/O(2) specificity factor (Omega). On the other hand, previous multi-step procedures, including the manipulation of radioisotope ((14)C and/or (3)H) and the chromatographic separation of the products, are inconvenient and may cause much random error. An improved assay procedure is presented therefore, which includes the spectrophotometric measurement of 3-phosphoglycerate-dependent NADH oxidation with a coupled enzyme system.