|
INVERTASE
Invertase is a yeast derived enzyme.
Invertase splits sucrose into glucose and
fructose.
The
official name for invertase is beta-fructofuranosidase (EC3.2.1.26),
which implies that the reaction catalyzed by this enzyme is the
hydrolysis of the terminal nonreducing beta-fructofuranoside residues
in beta-fructofuranosides. Note that alpha-D-glucosidase, which
splits off a terminal glucose unit, can also catalyze this reaction.
Note that sucrose can be hydrolyzed relatively easily; the reaction
proceeds in an acidic environment without the aid of
invertase.
Invertase is mainly used in the food (confectionery)
industry where fructose is preferred over sucrose because it is
sweeter and does not crystallize as easily. However, the use
of invertase is rather limited because another enzyme,
glucose isomerase, can be used to convert glucose to fructose more
inexpensively.
For
health and taste reasons, its use in food industry requires
that invertase be highly purified.
A
wide range of microorganisms produce invertase and can, thus, utilize sucrose as a
nutrient.
Commercially, invertase is biosynthesized chiefly by yeast strains of
Saccharomyces cerevisiae or Saccharomyces carlsbergensis. Even within
the same yeast culture, invertase exists in more than one form. For example,
the intracellular invertase has a molecular weight of 135,000 Daltons,
whereas the extracellular variety has a molecular weight of 270,000
Daltons.
In
contrary to most other enzymes, invertase exhibits relatively high activity over a
broad range of pH (3.5--5.5), with the optimum near pH=4.5. The
enzyme activity reaches a maximum at about 55ºC. The Michaelis-Menten
values of various enzymes vary widely, but for most enzymes Km is
between 2 mM and 5 mM. The Michaelis-Menten value for the free enzyme
is typically approx. 30 mM.
Enzyme inhibition is an extremely important area of
research in the medical field. For example, lead, mercury, other
heavy metals, and nerve gases are extremely poisonous to humans
because they are inhibitory to enzymes. For example, Pb^++ can easily
react with the sulfhydryl (-SH) groups in a protein:
protein-SH +
Pb++ + HS-protein -----> protein-S-Pb-S-protein +
2H+
|
