A reaction diagram is a plot of Gibbs free energy ($G$) vs. reaction progress for the substrate, product, transition state(s) and intermediates in a chemical reaction. A reaction diagram for a chemical reaction that is uncatalyzed as well as enzyme catalyzed is shown.
In the diagram, the blue line represents the uncatalyzed chemical reaction with the red line represents the enzyme-catalyzed reaction.
The value shown at point A on the graph represents
and the value shown at point B represents
. The value shown at point C represents
, the value at D stands for
, and finally, the value at point E is for