Kinetics of product inhibition during firefly luciferase luminescence

A theoretical and experimental analysis is made of the kinetics of product inhibition during firefly luciferase luminescence. Equations for competitive, noncompetitive, and uncompetitive inhibition are derived which are useful in determining inhibitory mechanism when the product inhibitor, or its concentration, is unknown and not subject to direct experimental manipulation. Comparisons of experimental data with predictions based upon the three inhibitory models show that product inhibition during luciferase luminescence is noncompetitive with respect to both luciferin and ATP as substrates. The competitive and uncompetitive models are inconsistent with experimental data. These findings provide the basis for using luminescence to measure ATP concentration continuously in in vitro biological systems such as isolated mitochondria.