The dependence of an initial
rate of reaction upon the concentration of a
substrate S that is present in large excess over the concentration of an enzyme or other
catalyst (or
reagent) E with the appearance of
saturation behaviour following the Michaelis-Menten equation:
,
where
is
the observed initial rate,
is its limiting value at
substrate
saturation (i.e.
), and
the substrate concentration when
.
The definition is experimental, i.e. it applies to any
reaction that follows an equation of this general form. The symbols
or
are sometimes used for
. The
parameters
and
(the '
Michaelis constant') of the
equation can be evaluated from the slope and intercept of a linear
plot of
vs.
(a '
Lineweaver–Burk
plot') or from slope and intercept of a linear plot of
vs.
('
Eadie–Hofstee plot'). A
Michaelis–Menten equation is also applicable to the condition
where E is present in large excess, in which case the concentration
appears in the equation instead of
.
The term has sometimes
been used to describe reactions that proceed according to the scheme:
in which case
(Briggs–Haldane conditions). It has more usually been applied
only to the special case in which
and
;
in
this case
is a true
dissociation constant
(Michaelis–Menten conditions).
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1140
PAC, 1996, 68, 149
(A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC
Recommendations 1996))
on page 172