Invertase is a yeast
derived enzyme. Invertase splits sucrose into glucose and fructose.
The official name for invertase is beta-fructofuranosidase (EC18.104.22.168),
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 55șC. 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+