Investigation of Catalytic Properties of Immobilized Enzymes and Cells by Flow Microcalorimetry - Advances in Biochemical Engineering Biotechnology - page 89

when cephalosporin C solution was fed into the system. The results shown in
Fig. 13 clearly demonstrate the superior stability of hardened calcium pectate
gel biocatalyst particles.
Another type of stability of immobilized biocatalysts is the retention of
activity after periodic use in batch processes,as has been reported previously for
penicillin acylase entrapped in polyacrylamide gel [40].This option can be used
to advantage for rapid monitoring of biocatalyst activity under conditions of
industrial application.Apart from the measurement of activity as an indication
of the necessity to replace the biocatalyst, the periodic analysis of the variation
of kinetic properties permits greater insight into deviation from the optimal
parameters.
Flow microcalorimetry allows the investigation of the relation between envi-
ronmental conditions and enzyme stability.For example,the influence of etha-
nol concentration on the stability of immobilized invertase was studied this
way [33].

5.4
Inhibition

Flow microcalorimetry was used for the investigation of product inhibition in
the urea-urease system [25].Inhibition was induced by the product of the reac-
tion. As mentioned above, this was a case in which the model had to be in the
form of differential equations, and the mass and heat balance had to be solved
by integration of these equations along the column. Another approach was
adopted in the investigation of invertase inhibition by products of sucrose
hydrolysis [33]. In this work, inhibition was observed qualitatively when
samples of sucrose with different concentrations of products (glucose or fruc-
tose) were fed into the immobilized enzyme column of the microcalorimeter.
Unfortunately, there are only a few reports nowadays about enzyme inhibition
analysis by flow microcalorimetry at the level of mathematical modeling pub-
lished in the literature.The majority of studies are concerned with the inhibitory
effect of substrate [27, 29-31]. In these investigations the mathematical treat-
ment of data is presented in simplified form, using the approaches described
above. Many kinetic models, including the inhibitory effects of compounds on
an enzyme,fit a kinetic equation of the following general form

V m c S

v(c Sb ,c Pb , P ) = (37)

59652

f(K m ,K i ,c S ,c i )

where c i is the inhibitor concentration and the function f in the denominator is
a general representation of denominators in kinetic equations involving inhi-
bition. Thus, when thermometric data are converted to reaction rates, the
following equation can be used for their description

1- e V m c S

v obs = h 759625 . (38)

e f(K m ,K i ,c S ,c i )