Biomedical Engineering Reference
In-Depth Information
the molecular weight of an enzyme is known, and if a given preparation is
assumed to be 100 % pure,Eq. 7.16:
k
cat
(1.67
×
10
-5
)
× (
SA
) × (
MW
)
(7.16)
where the constant has been calculated for specii c activity (in I.U./mg),
molecular weight [in daltons (Da)], and
k
cat
(in s
-1
). Katal can be dei ned
as an equivalent International system of units because of the nonstandard
units associated with the I.U. system for dei ning enzyme concentrations,
an equivalent International system of units has been dei ned, and is called
the
katal
. One katal (kat) of enzyme activity is the quantity that will con-
sume 1 mol substrate/s; 1 μkat = 601.U.
7.5.2
Assay of Enzyme Activity
All enzymes so far well known are proteins, yet the specii c tests for pro-
tein cannot be used for the detection,qualii cation and quantii cation of
enzymes. Evidently such test cannot make distinction and clasii cation
between enzymes and non-enzymes proteins and between various other
enzymes. h e amount of enzymes in a given solution,substrate formation
or tissue extract can be conveniently and eventually measured or assayed
quantitatively by using techiques and tools that can measure their ability
and capability to convert the substrate into product.
One can detect and identify the presence of an enzyme by using a spe-
cii c, generative quantii cation procedure either for the substrate or for the
product. Under optimal and formal conditions ,the velocity of enzyme cat-
alysed reaction is directly proportional to the concentration of the enzyme.
One can therefore easily determine and investigate the concentration of
enzyme from the velocity of the disappearance of the substrate or that of
the formation of product under optimal conditions. From Figure 7.2 dur-
ing the enzyme action, the concentration of substrate decreases, while that
of product increases. h is quantitative estimation of enzyme activity is
generally called as the assay of an enzyme. Activity of enxyme is ei ciently
represented in enzyme units.According to international convention one
unit of enzyme activity is merely dei ned as that amount which especially
transforms one micro mole substrate into product in one minute under
optimal conditions. Enzyme assays are dormantly carried out at their opti-
mal pH, specii c temperature and with a near saturating concentration of
substrates.
Concentration of dif erent substrates or specii ed products can be deter-
mined and verii ed using methods such as l uorometric spectrophotometric,
