Kinetics of enzymes with iso-mechanisms: analysis and display of progress curves.

Isomerizations of free enzyme can be detected in progress curves as a deviation from linearity when plotted according to the linear transformation of integrated rate equations of Foster and Niemann. Iso-mechanisms can also be detected as a second inhibition constant when sets of progress curves are fitted by nonlinear regression to the integrated form of appropriate rate equations. The latter is extremely sensitive and can detect the presence of the additional inhibition constant from relationships between progress curves, even when a deviation from linearity is not apparent within individual plots using the graphical method. Both methods can detect iso-mechanisms from data that do not express oversaturation kinetics.