A steady-state kinetic study on the catalytic mechanism of ribulose bisphosphate carboxylase from soybean

The catalytic mechanism of soybean ribulose bisphosphate carboxylase was examined, through a study of the steady-state kinetic behavior of the fully activated enzyme using short time assays. The effects of substrates, products, alternative products, and two dead-end inhibitors were investigated. High concentrations of both substrates were observed to lead to nonhyperbolic relationships: concentrations of bicarbonate greater than 15 mm inhibited and concentrations of ribulose bisphosphate greater than 0.2–0.5 mm stimulated enzyme activity over that expected from a hyperbolic fit to the data. The kinetic patterns obtained and the nonhyperbolic behavior of substrates are interpreted to suggest that the binding of substrates and the release of products follow a steady-state random mechanism. The substrate activation by ribulose bisphosphate is likely to be physiologically significant.