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Table 1. Recommended Symbols and their Units

Symbol	Meaning	Customary unit	Section of text	See notes below
[A]	concentration of substrate A	mol dm-3	2.1	1, 2, 3
[A]0.5 or [A]1/2	value of [A] at which v = 0.5 V	mol dm-3	4.2
[B]	concentration of substrate B	mol dm-3	2.1	1, 2, 3
[E]0 (or [E]t or [E]stoich)	stoichiometric concentration of active centres	mol dm-3	4.1	1, 3
h (or n H)	Hill coefficient	dimensionless
[I]	concentration of inhibitor I	mol dm-3	6.2	1, 2, 3
k	rate constant of any order n	(mol dm-3)1- n s-1
	pH-independent value of k	as k
k app	apparent value of k	as k	5.2, 6.4
k A, k B	specificity constants for A, B	mol-1 dm3 s-1	4.1
(etc.)	reciprocal Dalziel coefficient	(various)	5.1
k cat (or k 0)	catalytic constant	s-1	4.1, 5.2
ki,k-i	forward and reverse rate constants respectively for i th step	as k	3.1	4, 6
K i	inhibition constant (inhibition type unspecified)	mol dm-3	6.4
K iA	inhibition constant for A	mol dm-3	5.2
K ic	competitive inhibition constant	mol dm-3	6.4
k ij	rate constant for step from E i to E j	as k	3.1	4, 6
K iu	uncompetitive inhibition constant	mol dm-3	6.4
K m	Michaelis constant (or Michaelis concentration)	mol dm-3	4.2, 5.2
K mA	Michaelis constant for A	mol dm-3	4.2, 5.2
K s	substrate dissociation constant	mol dm-3	3.2
K sA	value of K s for substrate A	mol dm-3	3.2
k 0 (or k cat)	catalytic constant	s-1	4.1, 5.2
n H (or h)	Hill coefficient	dimensionless
[Q]	concentration of activator Q	mol dm-3		1, 2, 3
t	time	s	2.1
v	rate (or velocity) of reaction	mol dm-3 s-1	2.2
V (or V max)	limiting rate (or maximum rate, or maximum velocity)	mol dm-3 s-1	4.1, 5.2
v A	rate of consumption of A	mol dm-3 s-1	2.1
vi,v-i, vij	chemical flux (or chemiflux) through step with rate constant ki, k-i, kij	mol dm3 s-1	3.1
v max	true maximum value of v	mol dm-3 s-1	4.1
v Z	rate of formation of Z	mol dm-3 s-1	2.1
v 0	initial rate of reaction	mol dm-3 s-1	3.2
[Y]	concentration of product Y	mol dm-3	2.1	1, 2, 3
[Z]	concentration of product Z	mol dm-3	2.1	1, 2, 3
	coefficient of [A] i in numerator of generalized rate expression	(mol dm-3)1- i s-1
	coefficient of [A]i in denominator of generalized rate expression	(mol-1 dm3) i
	degree of activation	dimensionless
	degree of inhibition	dimensionless	6.3
	relaxation time	s
(etc.)	Dalziel coefficient	(various)	5.1
	for rate of reaction see Addendum 2		2.2

Notes:

1. Amount-of-substance concentration is abbreviated to concentration. This usage is acceptable in enzyme kinetics without special definition.

2. This symbolism can be extended to other reactants in an obvious way, e.g. K _mX is the Michaelis constant of X.

3. Other ways of indicating concentration, such as a for the concentration of A, are acceptable but must be explicitly defined.

4. Any numbering of rate constants must be in explicit relation to a reaction scheme.

5. Other pH-independent or apparent values may be represented similarly. e.g is the pH-independent value of V.

6. The rate constants for the ith step of a reaction may alternatively be represented as k _{2 i -1} and k _{2 i} instead of k_i and k_-i respectively (subject to note 4 above).

7. The initial rate may be represented by v, without subscript, when rates at other times are not in question. This rate is the steady-state rate extrapolated to zero time, not the true rate at zero time, which is normally undefined, because the rate of reaction is undefined during the transient phase of an enzyme-catalysed reaction.

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