Ping-pong reaction

In so-called ping-pong reactions products are released in a stepwise fashion. In a two-substrate reaction, the first substrate (S,) binds to the enzyme E and a product (Pi) is released, leaving the enzyme chemically modified (denoted E ), perhaps by a fragment of the substrate. Then the second substrate (S2) binds to the modified enzyme and is processed into a second product, P2, returning the enzyme to its native form. The scheme can be summarized as follows  

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Pinacolone, o-(diphenylphosphino)benzoyl-coordination chemistry, 2, 401 Ping-pong reactions copper(II) complexes, 5, 717 Piperidine, /V-hydroxy-metal complexes, 2, 797 P a values azole ligands, 2, 77 Plant roots amino acids, 2, 962 carboxylic adds, 2,962 Plants... 

Figure 8-11. Representations of three classes of Bi-Bi reaction mechanisms. Horizontal lines represent the enzyme. Arrows indicate the addition of substrates and departure of products. Top An ordered Bi-Bi reaction, characteristic of many NAD(P)H-dependent oxidore-ductases. Center A random Bi-Bi reaction, characteristic of many kinases and some dehydrogenases. Bottom A ping-pong reaction, characteristic of aminotransferases and serine proteases.

Figure 8-12. Lineweaver-Burk plotfora two-sub-strate ping-pong reaction. An increase in concentration of one substrate (S,) while that of the other substrate (SJ is maintained constant changes both thex and/intercepts, but not the slope.

In ping-pong reactions, one or more products are released from the enzyme before all the substrates have added. 

Figure 2.14 Reaction pathway for a bi-bi double-displacement (ping-pong) reaction mechanism.

With this protocol, ping pong reactions will yield at least one plot containing parallel lines. However, it is difficult with this procedure to obtain values for a number of the kinetic parameters (eg., Michaelis constants) for the reaction. An example of a system studied with this procedure is provided by E. coli CoA-linked aldehyde dehydrogenase. See Frieden Protocol... 

A mathematical equation indicating how the equilibrium constant of an enzyme-catalyzed reaction (or half-reaction in the case of so-called ping pong reaction mechanisms) is related to the various kinetic parameters for the reaction mechanism. In the Briggs-Haldane steady-state treatment of a Uni Uni reaction mechanism, the Haldane relation can be written as follows ... 

In ping pong reactions, Haldane relations can also be written for the individual half-reactions. In such cases, Haldane expressions assist in analyzing isotope exchange studies involving these partial reactions. 

Another important characteristic of ping pong reaction is the presence of exchange reactions in the absence of other substrates. See Isotope Exchange at Equilibrium Multisite Ping Pong Bi Bi Mechanism Half-Reaction Substrate Synergism... 

A procedure that assists in the characterization of binding mechanisms for sequential (/.e., non-ping pong) reactions . The same general initial rate expression applies to the steady-state ordered Bi Bi reaction, the rapid-equilibrium random Bi Bi reaction, and the Theorell-... 

A ping-pong reaction occurs, for example, when a phosphate-transferring enzyme, such as phosphoglycerate mutase, is phosphorylated by one substrate to form a phosphorylenzyme (E—P in equation 3.55), which then transfers the... 

In a two-substrate reaction similar to that catalyzed by hexokinase, two basic mechanisms may be at work. First, a ping-pong reaction may be occurring in which the enzyme shuttles between a stable enzyme intermediate, such as a phosphorylated enzyme, and a free enzyme. Second, the reaction may be sequential, in which case no reaction occurs until both substrates are on the enzyme. There are two types of sequential mechanisms. If one substrate cannot bind until after the addition of the other substrate the mechanism is said to be ordered. However, if they can combine in any order the mechanism is said to be random. The various kinetic methods for distinguishing between these mechanistic forms have been summarized by Cleland (52). The evidence for and against these possible kinetic schemes will now be summarized for yeast hexokinase. 

Double-reciprocal plots in ping-pong reactions (W0 vs 1/[A0]) at constant but different concentrations of B give parallel straight lines that never intersect (Figure 5.10B). An example of such reactions are those catalyzed by transaminases (Chapter 20) ... 

In double-displacement, or Ping-Pong, reactions, one or more products are released before all substrates bind the enzyme. The defining feature of double-displacement reactions is the existence of a substituted enzyme intermediate, in which the enzyme is temporarily modified. Reactions that shuttle amino groups between amino acids and a-keto acids are classic examples of double-displacement mechanisms. The enzyme aspartate aminotransferase (Section 23.3.1) catalyzes the transfer of an amino group from aspartate to a-ketoglutarate. 

Fig. 7.14. Double reciprocal plots for ping-pong reactions run at several fixed concentrations of B.

The enzyme—substrate interactions can proceed by either single-displacement or double-displacement reactions (commonly known as ping-pong reactions). A substrate reaction proceeding by way of a single-displacement reaction can be shown by... 

Transamination reactions have been described as ping-pong reactions. Using the reaction of alanine with a-ketoglutarate, indicate how this ping-pong reaction works. 

Steady-state kinetics have been used to determine the kinetic mechanisms of many of these enzymes. The questions that have been primarily addressed are the sequence of steps that occur in substrate binding prior and subsequent to the catalytic reaction and the potential formation of covalent enzyme intermediates. Classical interpretation of kinetic analyses has been the determination of the relevant reactions occurring via a random or an ordered sequential reaction, or if the reaction is a double-displacement or Ping-Pong reaction. In the former case, phosphoryl transfer occurs in the ternary complex that contains enzyme, phosphoryl donor, and phosphoryl acceptor. In the latter case, enzyme reacts with... 

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