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INTRODUCTION.

Contents of Section

• 1. Introduction
• 2. Basic definitions
• 2.1 Rates of consumption and information
• 2.2 Rate of reaction
• 2.3 Elementary and composite reactions
• 3. Order of reaction and rate constant
• 3.1 Numbering of reactions
• 3.2 Steady-state hypothesis
• References for this section

INTRODUCTION

Recommendations on the symbols and terminology of enzyme kinetics were previously made in conjunction with the recommendations of the Commission on Biochemical Nomenclature and Classification of Enzymes, and were published in Enzyme Nomenclature (1972) [1] and in earlier editions. During preparation of Enzyme Nomenclature (1978) [2] by NC-IUB it was agreed that the symbols and terminology of enzyme kinetics were properly distinct from the nomenclature of enzymes and should therefore be omitted from a compilation of enzyme names. In consequence the 1972 recommendations [1] have remained in operation even though they take little account of the developments of the subject in the past two decades, particularly the increased interest in reactions with two or more substrates. Accordingly, during 1978-1979 the views of numerous biochemists active in enzyme kinetics were solicited by NC-IUB and subsequently a panel was set up to make new recommendations.

To minimize differences between chemical and biochemical practice, the Report on Symbolism and Terminology in Chemical Kinetics [3] produced by IUPAC in 1980 has been followed where appropriate. Such differences as remain are the consequence of long-standing biochemical practice or of the fact that enzyme-catalysed reactions usually have simple overall stoichiometries and take place at constant pressure in the liquid phase and so require little attention to some details that may be crucial in chemical kinetics.

Certain conflicts that have greatly exercised some biochemists now seem less important than they may have done in the past. For example, because of the great diversity of enzyme mechanisms it is unlikely that any one system of numbering rate constants can satisfy all possible needs. It is much more important that rate constants be clearly defined in the context in which they are used than that they should satisfy any universal system Thus although this report follows the IUPAC recommendations [3,4] in its examples for illustration it is not implied that these should be used without definition or in all circumstances.

We have adopted the general policy of taking an operational approach to definitions, terms and symbols, rather than basing them on assumed mechanisms. In other words, definitions refer to what one observes, not to the way it is interpreted. This seems to be the safest course in kinetics, and particularly in enzyme kinetics, as conclusions about mechanisms often have to be revised in the light of further investigations, whereas the observations, if they are properly carried out, do not. Definitions based on what is actually observed are therefore on a sounder and more lasting basis than those that depend on an assumed mechanism. In Section 11 we do, however, consider mechanisms briefly.

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