Kinetic mechanisms Cleland notation

Restricting ourselves to the rapid equilibrium approximation (as opposed to the steady-state approximation) and adopting the notation of Cleland [158 160], the most common enzyme-kinetic mechanisms are shown in Fig. 8. In multisubstrate reactions, the number of participating reactants in either direction is designated by the prefixes Uni, Bi, or Ter. As an example, consider the Random Bi Bi Mechanism, depicted in Fig. 8a. Following the derivation in Ref. [161], we assume that the overall reaction is described by vrbb = k+ [EAB — k EPQ. Using the conservation of total enzyme... 

Haldane relationships are relationships between the equilibrium constant and the various kinetic constants defined for a given mechanism. They exist because we define for each mechanism more kinetic parameters than there are independently determinable parameters. They are of two types, kinetic and thermodynamic, and every mechanism has at least one of each. Thermodynamic Haldanes consist of the cross product of reciprocal dissociation constants for the substrates and dissociation constants for the products (i.e., the product of equilibrium constants for each step in the mechanism). For mechanisms with at least three substrates, the Cleland notation defines dissociation constants as K, values (i.e., /fia, ib, K c, etc.), but for Ordered Uni Bi and Bi Bi mechanisms, Cleland defined the dissociation constants of the inner substrates differently (4). The dissociation constants for A and Q were and /(jq, but that for B was... 

All kinetic mechanisms can be presented in shorthand notations the most popular is that proposed by Cleland (1963). However, the reader is warned that he or she wiU find other systems in the literature, as weU as in this book, and will have to examine the definitions given for the kinetic constants in each case. 

Three possible kinetic mechanisms for a two-substrate/two-product reaction depicted in Cleland notation. Substrates are designated as A and B , products as C and D while E represents the enzyme and E is a covalently modified enzyme that forms transiently as part of the normal catalytic pathway in the ping-pong mechanism. 

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See also in sourсe #XX -- [ ]

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