Enzymes in food technology – introduction - Enzymes in Food Technology - page 11

1.5.6.2 Uncompetitive inhibition

In uncompetitive inhibition, the inhibitor cannot bind to the free enzyme, but only to the ES
complex. The EIS complex thus formed is enzymatically inactive. This type of inhibition is
rare, but may occur in multimeric enzymes.

1.5.6.3 Non-competitive inhibition

Non-competitive inhibitors are considered to be substances which, when added to the enzyme,
alter the enzyme in a way that it cannot accept the substrate.
Non-competitive inhibitors can bind to the enzyme at the same time as the substrate; that
is, they never bind to the active site. In this way a complex is formed of enzyme, inhibitor
and substrate (EIS). Both the EI and EIS complexes are enzymatically inactive. Because the
inhibitor cannot be driven from the enzyme by higher substrate concentration (in contrast to
competitive inhibition), the apparent V max changes. But because the substrate can still bind
to the enzyme, the K m stays the same.

1.5.6.4 Mixed inhibition

This type of inhibition resembles the non-competitive, except that the EIS complex has
residual enzymatic activity.
In many organisms, inhibitors may act as part of a feedback mechanism. If an enzyme
produces too much of one substance in the organism, that substance may act as an inhibitor
for the enzyme at the beginning of the pathway that produces it, causing production of the
substance to slow down or stop when there is sufficient amount. This is a form of negative
feedback. Enzymes which are subject to this form of regulation are often multimeric and
have allosteric binding sites for regulatory substances. Irreversible inhibitors react with the
enzyme and form a covalent adduct with the protein.

1.6 INDUSTRIAL ENZYMES

For centuries, enzymes have been employed in a variety of applications such as beer and
cheese production. Both in the past and currently, enzymes have been derived from natural
sources such as the tissue of plants and animals; Table 1.1 summarizes these. However, over
the years, advancements in biotechnology have resulted in newer and more highly efficient
varieties of enzymes.
The industrial success of enzymes can be attributed to certain key benefits that enzymes
offer in comparison with chemicals. The combination of catalytic function, specificity and
the ability to work under reasonably mild conditions makes enzymes the preferred catalyst
in a variety of applications.
Industrial enzymes are prepared and commercialized as partly purified or 'bulk' enzymes,
as opposed to highly purified enzymes for analytical or diagnostic use. Industrial enzymes
may be derived from a wide variety of plant, animal or microbial sources, although most pro-
duction processes rely on microbial sources. Microbial enzymes are either extracellular, such
as the proteases and carbohydrates, which account for a large proportion of total sales, or in-
tracellular, such as glucose oxidase. Intracellular enzymes usually remain associated with the
cell and therefore have to be released, unless the microorganism itself is used as the catalyst.