Range Of Buffer Concentrations Research Articles

Kinetics of binding of reduced nicotinamide adenine dinucleotide phosphate to the rat liver fatty acid synthetase complex

A 5-fold variation in each of the dissociation constants for the binding reactions between NADPH and the two pairs of NADPH-binding sites possessed by rat liver fatty acid synthetase occurred in response to changes in phosphate buffer concentration over the range 0.12–0.20 m. Estimates of the rate constants for the binding reaction and for the dissociation of the enzyme-coenzyme complex have been obtained for each pair of binding sites over a range of buffer concentrations. This was accomplished using stopped-flow fluorescence enhancement. The rate constants for the binding reactions were found to be approximately 1 × 10 7 m −1, sec −1 and 1.2 × 10 6 m −1, sec −1 for the reactions occurring at the stronger and weaker pairs of binding sites, respectively. Furthermore, these values remained substantially constant over the range of phosphate buffer concentrations tested. Conversely, the rate constants for the dissociation reactions of the enzyme-NADPH complex at the stronger and weaker pairs of binding sites were found to vary in response to buffer concentration changes over the ranges 1–9 sec −1 and 10–30 sec −1, respectively.