Modified Cleland notation

Substrates are designated by the letters A, B, C, D,..., in the order in which they bind to the enzyme, and products are designated by P, Q, R, S,..., in the order in which they release from the enzyme. Enzyme forms incapable of unimolecular reaction with liberation of a substrate or product or isomerization into such a form are called stable enzyme form and are designated by E, F, G, H,... Enzyme forms capable of unimolecular reaction with liberation of a substrate or product or isomerization into such a form are called transitory complexes and are designated by such as EA, EAB, FB, HQ.

The number of kinetically important substrates or products in a mechanism are designated by the syllables Uni, Bi, Ter, and the number of reactants involved in the reaction in one direction will be the reactancy in that direction. Thus the reaction with two substrates and two products is called Bi Bi and spoken of as being bireactant in both directions. The reaction where there is one substrate and two products will be unireactant in the forward direction and bireactant in the reverse, and is called Uni Bi. Reactions with three substrates and two products are Ter Bi, and reactions with three substrates and three products are Ter Ter.

The order of bind of substrates and release products within the reaction sequence is described as follows: Mechanisms where all substrates must add to the enzyme before any products are released will be designated "sequential". Such mechanisms are called "Ordered" (for example, Ordered Bi Bi ) if the substrate add in obligatory order and the products leave similary, and "Random" (for example, Random Bi Bi) if the substrates do not react in obligatory order. When one or more products are released before all substrates have binded to the enzyme, the enzyme exist in two or more stable forms between which it oscillates during the reaction. Such mechanisms are called "Ping-Pong" (for example, Ping-Pong Bi Bi). If there is no central complex formed at all, as in the mechanism proposed by Theorell and Chance for alcohol dehydrogenase (H. Theorell and B. Chance, Acta Chem. Scand., 1951, v.5, p.1127) the mechanism is different from Ordered Bi Bi and is called "Theorell Chance" (see example here ) mechanism.

The ERM version is used also nomenclature that is different from the original in the following two points:

The elegant method of King and Altman (King E. L., Altman C. A., J. Phys. Chem., 1956, v.60, p.1375-1378) allows the steady-state rate equation for mechanisms of considerable complexity to be written down in terms of the individual rate constatnts without going through messy algebraic expansions of large determinants. Cleland's approach show how rate equation expressed in terms of rate constants can be transformed into equation expressed entirely in terms of measurable kinetic constants.

Russian Academy of Science

Institute of Theoretical and Experimental Biophysics

Laboratory of Metabolic Simulation and Bioinformatics

Pushchino, Moscow reg., Russia, 142290.