Invertase

Sucrase is one of the glycosidases. Invertase (fructofuranoside fructohydrolase) (fructofuranoside fructohydrolase) specifically catalyzes the hydrolysis of β-D-fructofuranoside bonds in non-reducing sugars. Sex. Not only can catalyze the hydrolysis of sucrose to produce glucose and fructose, but also can catalyze the hydrolysis of raffinose to produce dense disaccharide and fructose.

Figure 1. Protein structure of invertase.

Introductions

One of glycosidases. An enzyme that catalyzes the hydrolysis of sucrose into fructose and glucose. It is widely found in animals, plants and microorganisms, and is mainly obtained from yeast. Since Bertholet discovered invertase from Sacchacomyces Cerevisiae in 1860, it has been extensively studied. Invertase (specifically catalyzes the hydrolysis of α-fructofuran glycoside bonds in non-reducing sugars, is relatively specific. It can not only catalyze the hydrolysis of sucrose to produce glucose and fructose, but also the hydrolysis of raffinose to produce dense disaccharides and fructose. The enzyme exists in two forms on the outside and inside of the yeast cell membrane. It is called external yeast invertase in the outer cell wall of the cell membrane, and its activity accounts for most of the activity of the sucrase, which contains 50% ~ 70 ( Mass Fraction) The glycoprotein of the sugar component; what is called internal yeast invertase in the cytoplasm inside the cell membrane contains a small amount of sugar. The protein part of the two enzymes is a double subunit (dimer) structure. The amino acid composition of the two forms of enzymes is different. Each subunit of the outer enzyme has two more amino acids than the inner enzyme-serine and methionine. The external enzyme is about 270KD (or 220KD, depending on the source of yeast) and the internal enzyme is about 135KD. Although the two enzymes are quite different in composition, the substrate specificity and kinetic properties are still very similar, but because the internal enzyme content is very small, it is extremely difficult to extract.

Functions

Sucrose is catalyzed by sucrase. Hydrolyzed into two reducing sugars, D-glucose and D-fructose. Invertase plays a major role in plant transportation and carbohydrate metabolism. It also plays an important role in osmotic regulation, stress-resistant growth and reproduction, and signal transmission.

Classification

According to the subcellular position of sucrase in plants, sucrase can be divided into liquid cell type sucrase, cytoplasmic sucrase and cell wall sucrase. The first two are also called intracellular invertase, and the cell wall invertase is also called extracellular invertase. Different invertases need different optimal pH values for the reaction, so invertase can be divided into acid invertase and neutral / alkaline invertase. Liquid cell type sucrase and cell wall type sucrase have the highest catalytic efficiency at pH 4.5 to 5.0, so they are also called acid sucrase. The optimal pH value of cytoplasmic sucrase for hydrolyzing sucrose is neutral or slightly alkaline, so it is called neutral/alkaline sucrase. According to its solubility, sucrase can be divided into soluble sucrase (including liquid cell sucrase and cytoplasmic sucrase) and insoluble sucrase (cell wall sucrase).

Purification of invertase

The crude enzyme solution was purified by O-Sepharose FF anion exchange column chromatography. The crude enzyme solution with high sucrase activity extracted by the SDS extraction method was precipitated with 50% ethanol by mass, dissolved and dialyzed, and then passed through a Q-Sepharose FF anion exchange column (with pH 7.0, 0.05 mol/L Tris-HCl buffer is fully equilibrated). It was eluted with a NaCI solution with a linear gradient of 0 to 1 mol/L and 60 min (containing pH values of 7.0 and 0.05 mol / L% s-HCI buffer). The volume flow rate is 0.5 mL/min, and each mL is collected. Measure the invertase activity and protein content of each tube eluate, and combine several tube effluents with high invertase activity. The effluent is desalted by dialysis and dried in vacuum to be purified yeast invertase.

Common glycosidases

1. Alpha-mannosidase. The mannosidase involved in the N-glycosylation process can be divided into α-mannosidase and β-mannosidase according to the difference of the hydrolysis bond they catalyze There are more than 20 cDNAs, including 6 from humans. Alpha-mannosidase is mainly present in the endoplasmic reticulum, Golgi apparatus, lysosome and other cytoplasmic organelles. Its function is to splice different mannose residues connected to the ends of the oligosaccharide structure, forming high-mannose type, complex type, hetero Combined N-oligosaccharides.

Figure 2. Alpha-mannosidase.

2. Arabinosidase. The now purified arabinosidase, according to its amino acid sequence, according to the similarities and differences of the substrate specificity, arabinosidase can be divided into two categories: arabinosidase A generally degrades the arabinose at the end, and arabinosidase B Degradation of the arabinose group at the end can also cut the arabinose side branch.

3.  β-xylosidase. Beta-xylosidase is widely distributed in nature, and has been isolated from microorganisms and higher plants such as bacteria, actinomycetes and fungi (including yeast).

4.  Chitosanase. Chitotriosidase (CT) is a functional chitinase. Humans were thought to have no and cannot degrade chitin components, so chitinase has long been used as a target for chemotherapy drugs, such as antifungal drugs, antimalarial drugs, and insecticides.

5.  Thioglycosidase. Microbial glycosidases come from a wide range of sources, and some glycosidases not only have hydrolytic activity, but also have transgenic activity. This property makes them an important tool for carbohydrate synthesis and is used for large-scale synthesis of various O-glycosides.

Reference

1. Whitehead, A. M, et al. Study to compare the enzyme activity, acid resistance and dissolution characteristics of currently available pancreatic enzyme preparations. Pharmaceutisch Weekblad Scientific Edition. 1998, 10 (1): 12–16.