Biomedical Engineering Reference
In-Depth Information
where K for the enzymes-substrate complex and
K
iS
is the ai nity of the
inhibitor for enzyme.
It is shown that:
KS
[]
[]
m
IC
(7.7)
50
K
S
KK
m
iS
iI
If the inhibitor binds equally in a good way to the enzyme like the enzyme-
substrate complex,
K
iS
=
K
iI
=
K
i
and the equation simplii es to:
IC
50
=
K
i
(7.8)
Alternatively, if as is ot en the case [
S
]
〉〉
m
and
m
/
[
S
]
〈〈
iS
/
K
iI
, the equa-
tion reduce to:
K
IC
KSKK
iS
(7.9)
50
[]
m
iS
iI
Again, if
m
/
[
S
]
〈〈
iS
/
K
iI
, then:
IC
50
=
K
i
(7.10)
IC
50
is independent of substrate concentration and equal to K in the case
of uncompetitive inhibition, provided that [
S
]
〉〉
m
.
It is not always conve-
nient to maintain a substrate concentration that is extremely higher than
the
m
because this may vary the ef ect of weaker inhibitors.
7.5.1
Enzyme Units and Concentrations
h e molar units and mass per unit volume are the identical manner with
nonanalytic species through which enzyme concentration may be repre-
sented. h e percentage purity of the enzyme preparation, the molecular
weight of the enzyme, and the mass and volume of the solution prepared
are the information required for the calculation which is minimal. As
nothing is noticed about the catalytic power of the solution prepared, the
enzyme concentration is rarely represented in this way.
h e number of
International Units
(I.U.) per unit volume commonly
depicts the concentration of an enzyme solution. h e International Units is
