Rate constants for the forward and reverse reactions in the multistep enzyme-
catalyzed process
should be designated by k
+n
and k
–n
, respectively. The Michaelis constant (K
m
) is defined as substrate
concentration ([S]) which corresponds to v = V/2, where V (or V
max
)
is the
reaction rate under conditions of
the enzyme saturation with the substrate and v is the rate of product appearance or substrate disappearance.
For reactions involving two substrates (A and B) K
A
= [A] at v = V/2 and [B] extrapolated to infinity; the
value of [A] at which v = V/2 at the final concentration (which should be specified) of B should be referred
to as an apparent
Michaelis constant for A (
K
A
m,app
). Other parameters used in enzyme kinetics include:
K
s
, dissociation constant for enzyme–substrate complex; K
i
, dissociation constant for enzyme–inhibitor
complex; [I]
50
, inhibitor concentration at which the rate is decreased by half; h, Hill
coefficient (parameter
in the Hill equation used to describe S-shaped dependences of v on the substrate or inhibitor
concentrations) [see also “Recommendations on Symbolism and Terminology in Enzyme Kinetics”
published in Arch. Biochem. Biophys., 224, 732-740 (1983)].
Substance amount, molecular mass, Dalton, and molar concentration. The SI unit of the
substance amount (n) is mole (abbreviated mol), i.e., the substance amount containing the same number of
structural units (molecules, atoms, ions, electrons, etc.) as the number of carbon
atoms in 0.012 kg of
12
C
(the Avogadro’s constant, N
A
= 6.02·10
23
per mol, gives the number of
structural units in the mole of any
substance). Molar mass (M) is the mass of 1 mol of the substance (m/n), and its dimension is g/mol or
kg/mol. Obviously, mass (m, g), amount (n, mol), and molar mass (M, g/mol) are different terms which are
related to one another with the relationship m = nM. There are two preferred ways of specifying the mass
of a biochemical
entity: relative molecular mass (M
r
, formerly “molecular weight”) is the ratio of the
molecule
mass to 1/12 of the atom
12
C atom. Hence, it is dimensionless. Molecular mass is the mass of
one molecule of a substance expressed in Daltons; the Dalton is defined as 1/12 of the
12
C atom,
or M/N
A
.
Thus, it may be said that a protein has a relative molecular mass of 50,000 (M
r
=
50,000) or a molecular
mass of 50,000 Daltons (better, 50 kDa), and may be referred to as the
50,000-M
r
protein or the 50-kDa
protein. It is not correct to express M
r
in Daltons, either M
r
or
molecular mass (kDa) should be used
throughout the paper.
Solutions should be described in terms of molarity (M, mM, µM, etc.), i.e., the number of the
substance moles in 1 liter of the solution, not normality (N). The decimal system should be used,
e.g., 0.25 M HCl. Concentration expressed in % must be defined as w/w, w/v, or v/v, e.g., 5% (w/v) means
5 g/100 ml. For salts solutions with concentration expressed in %, it should be indicated whether the
compounds were hydrated or anhydrous.
Nucleotide sequences. Authors should remember that nucleotide sequence should be determined
in both DNA chains. A clear description of such determinations and data on the complete sequence will
suffice.
Metric prefixes in tables and figures. Authors must be careful when using exponents to avoid
numbers with too many digits in the headings of tables and in figures. This is illustrated by the following
examples: 1) a concentration 0.00015 M may be expressed as 15·10
–5
M, but it is preferable to give it
using a prefix, as 0.15 mM or 150 µM; it is appropriate to express concentration of 0.15 in the table or
figure under the heading “Concentration, mM” or 150 under “Concentration, µM”, or 15 under
“Concentration × 10
5
, M” (but not 15 under the heading “Concentration, M × 10
–5
”); 2) listing of 2 under
the heading “10
3
k” means k = 0.002, and 2 under the heading “10
–3
k” means k = 2000; 3) complex
quantities are treated similarly; a value of 200 M
–1
for 1/[S] would appear as “2” under the heading “10
–
2
/[S], M
–1
” or as “0.2” under the heading “1/[S], mM
–1
”. Concentrations may conveniently be indicated by
square brackets.
The following decimal prefixes and their symbols should be used for multiples and subdivisions of
units: