Biochemistry: The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

Enzymes: Protein Catalysts of Cells
Enzyme Inhibition and Activation
Using Inhibitors to Study Mechanisms of Enzymatic Reactions

A substrate analogue binds exclusively to only one of the two forms of an enzyme catalyzing a multisubstrate enzymatic reaction that proceeds via a ping-pong mechanism. Much like non-competitive inhibition, the 1/v versus 1/[S] plots, constructed at various fixed inhibitor concentrations, yield a family of parallel lines. Obtaining such a family of lines for a given enzyme may indicate a ping-pong mechanism at play. (It should be noted, however, that parallel lines in {1/[S]; 1/v} coordinates can also arise during the inhibition of Enzymes operating via an ordered sequential mechanism.) When considering a bimolecular enzymatic reaction characterized by ordered substrate binding [Scheme (6-34)], a natural question arises: which of the two reacting substrates binds first? If the concentration of one substrate is held constant while varying concentrations of an analogue of this substrate—incapable of catalytic conversion—are added to the system, plotting the reciprocal velocity versus the reciprocal concentration of the other substrate yields parallel lines if and only if the fixed-concentration substrate is B (the substrate that binds second) and I is its analogue. The substrate that binds first (A) is the one whose concentration is varied in the experiment.

Product inhibition (Section A, 9) also provides valuable insight into The Mechanism of an enzymatic process. For instance, plotting 1/v versus 1/[A] for an ordered sequential mechanism (6-34) reveals that the product competes with A, yielding a family of lines characteristic of competitive inhibition. Meanwhile, the 1/v versus 1/[B] plots in the absence and presence of product Q will exhibit...

a pattern characteristic of non-competitive inhibition. In other words, a competitive relationship exists solely between A and Q. Product inhibition is also observed for enzymes operating via a ping-pong mechanism due to The formation of non-productive complexes (Section A, 10, 6).