Irreversible ping-pong mechanism

Studies of product inhibition357,358 and initial velocity359 of the dehydrogenase reaction are consistent with a hexa uni ping-pong mechanism,359 which requires that an irreversible step of the process should occur in the reaction sequence prior to addition of the second molecule of NAD to the enzyme. The irreversible step is, most probably, formation of the uronic acid (90a) from the aldehyde 93, and several mechanisms may be written to explain the kinetics ob-... 

Figure 6.15. Ping-pong mechanism with quasi-equilibria binding steps and irreversible reaction steps.

The steady state kinetics of arsenite oxidoreductase from A. faecalis indicate a so-called double displacement (or ping-pong ) mechanism (15) in which the enzyme cycles between oxidized and reduced forms in its reaction with arsenite and azurin (or cytochrome c). This overall kinetic scheme is common in redox-active proteins. Arsenite must bind, the oxygen atom transfer chemistry take place, and arsenate dissociate before the subsequent reaction of a second molecule of substrate. Since arsenate is not an inhibitor of arsenite oxidoreductase (43), product dissociation must be effectively irreversible. The turnover number (kcai) of 27 sec and for arsenite of 8 pM are reasonable parameters for the detoxification of arsenite, especially since A. faecalis is able to survive in at least 80 mM (1%) sodium arsenite. The considerable catalytic power of the enzyme is reflected by the kinetic parameter k JK of 3.4 X 10 M sec , which is fairly close to the diffusion-controlled maximum of 10 -10 M sec for proteins in... 

Enzymes are more commonly involved in the reaction of two substrates to form products. In this problem, analyze the specific case of the ping pong hi hi mechanism [W. W. Cleland, Biochim. Biophys. Acta, 67 (1963) 104] for the irreversible enzymatic conversion of... 

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