β-Fructofuranosidase is an

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

that catalyzes the

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

(breakdown) of the table sugar sucrose into

fructose Fructose (), or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and gal ...

and

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

. Sucrose is a fructoside. Alternative names for β-fructofuranosidase include invertase, saccharase, glucosucrase, β-fructosidase, invertin, fructosylinvertase, alkaline invertase, and acid invertase. The resulting mixture of fructose and glucose is called inverted sugar syrup. Related to invertases are sucrases. Invertases and sucrases hydrolyze sucrose to give the same mixture of glucose and fructose. Invertase is a glycoprotein that hydrolyses (cleaves) the non-reducing terminal β-fructofuranoside residues. Invertases cleave the O-C(fructose) bond, whereas the sucrases cleave the O-C(glucose) bond. Invertase cleaves the α-1,2-glycosidic bond of sucrose. For industrial use, invertase is usually derived from

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

. It is also synthesized by bees, which use it to make

honey Honey is a sweet and viscous substance made by several species of bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of pl ...

from nectar. The temperature optimum is 60 °C and a pH optimum is 4.5. Sugar can be inverted by

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

but this is not suitable for food-grade products and enzymic hydrolysis is preferred. Invertase is produced by various organisms such as yeast, fungi, bacteria, higher plants, and animals. For example: ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungal microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have be ...

'', '' Saccharomyces carlsbergensis'', '' S. pombe'', ''

Aspergillus ' () is a genus consisting of several hundred mold species found in various climates worldwide. ''Aspergillus'' was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli. Viewing the fungi under a microscope, Miche ...

'' spp, '' Penicillium chrysogenum'', ''

Azotobacter ''Azotobacter'' is a genus of usually motile, oval or spherical bacteria that form thick-walled cysts (and also has hard crust) and may produce large quantities of capsular slime. They are aerobic, free-living soil microbes that play an impo ...

'' spp, '' Lactobacillus'' spp, ''

Pseudomonas ''Pseudomonas'' is a genus of Gram-negative bacteria belonging to the family Pseudomonadaceae in the class Gammaproteobacteria. The 348 members of the genus demonstrate a great deal of metabolic diversity and consequently are able to colonize a ...

'' spp etc.

Applications and examples

Invertase is used to produce inverted sugar syrup. Invertase is expensive, so it may be preferable to make fructose from glucose using glucose isomerase, instead. Chocolate-covered candies, other cordials, and fondant candies include invertase, which liquefies the sugar.

Inhibition

Urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

acts as a pure non-competitive inhibitor of invertase, presumably by breaking the intramolecular

hydrogen bond In chemistry, a hydrogen bond (H-bond) is a specific type of molecular interaction that exhibits partial covalent character and cannot be described as a purely electrostatic force. It occurs when a hydrogen (H) atom, Covalent bond, covalently b ...

s contributing to the

tertiary structure Protein tertiary structure is the three-dimensional shape of a protein. The tertiary structure will have a single polypeptide chain "backbone" with one or more protein secondary structures, the protein domains. Amino acid side chains and the ...

of the enzyme.

Structure and function

Reaction pathway

Invertase works to catalyze the cleavage of sucrose into its two monosaccharides, glucose and fructose. This specific invertase (β-fructofuranosidase) cleaves the molecule from its fructose end resulting in the two monosaccharides. It does this by adding a hydrogen ion to the glycosidic atom by an imidazolium cation. From there, an unstable intermediate carbonium ion will be left behind by the leaving of an alcohol group. Finally, the nucleophilic oxygen atom from alcohol or water will attack the C-2 cation which will leave behind a fructose molecule. The active-site carboxylate anion will take action to help keep the unequal balance of electrons stabilized throughout this process.

Purpose of invertase in yeast

As mentioned previously, invertase is commonly found in bakers' yeast. One of the main reasons that bakers use this yeast is to help bread rise, but another reason is to help influence the increase of sugar in bread. This function is able to happen due to the presence of invertase since glucose and fructose is sweeter than sucrose is. When looking at invertase across different species of yeasts, it has been known to be more active in some than others. The yeast that invertase is more active in is the yeast bakers use due to its higher sweetness levels.

Known crystal structures

Continuing to look at invertase through ''Saccharomyces'', it can be seen that it has a unique structure; that structure being an octameric quaternary structure. Within the octameric quaternary structure, two dimerization types can be seen that in turn, form the octamer structure. Dimerization is an important aspect of protein folding due to it increasing the affinity of substrate binding. The crystal structure shows that the invertase is made up of eight subunits. The octamer shape is made up of two different types of dimers, a “‘closed’ arrangement” and an “‘open’ assembly” dimer. Each of these types has two subunits located opposite from each other in the structure. The “‘closed’ arrangement” dimers have fourteen out of the 32 hydrogen bonds made between the catalytic domain which creates a tighter pocket for the ligand; in turn, this makes it more stable. In contrast, the “‘open’ assembly” dimers only have a few hydrogen bonds in the catalytic domain, and the interactions that strengthen the pocket come from the salt bridges between Asp-45 and Lys-385. With the weaker interactions being in the “‘open’ assembly", it causes more instability that results in a lower denaturing temperature and lower durability at high-speed centrifugation. The way that the two dimers assemble, creates an antiparallel β sheet composed of β sandwiches made from two β sheets.

Known active sites

While the focus has been on invertase in ''Saccharomyces'', one of the known active sites is in the invertase in ''Bifidobacterium longum'' and is located within the β-propeller domain. The β-propeller domain is the inside the funnel created by five blades. Some amino acids to note are, Asp-54 and Glu-235, which are on the first strand of blades 1 and 4, along with Asn-53, Gln-70, Trp-78, Ser-114, Arg-180 and Asp-181 in the fructofuranoside ring.

References

External links

* {{Authority control EC 3.2.1 Food additives E-number additives