Topic summary
Β-Amylase
β-Amylase (EC3.2.1.2, saccharogen amylase, glycogenase) is an enzyme with the systematic name4-α-D-glucan maltohydrolase. It catalyses the following reaction:
- Hydrolysis of (1→4)-α-D-glucosidic linkages in polysaccharides so as to remove successive maltose units from the non-reducing ends of the chains
This enzyme acts on starch, glycogen and related polysaccharides and oligosaccharides producing beta-maltose by an inversion. Beta-amylase is found in bacteria, fungi, and plants; bacteria and cereal sources are the most heat stable. Working from the non-reducing end, β-amylase catalyzes the hydrolysis of the second α-1,4 glycosidic bond, cleaving off two glucose units (maltose) at a time. During the ripening of fruit, β-amylase breaks starch into maltose, resulting in the sweet flavor of ripe fruit.
β-amylase is present in an inactive form prior to seed germination. Many microbes also produce amylase to degrade extracellular starches. Animal tissues do not contain β-amylase, although it may be present in microorganisms contained within the digestive tract. The optimum pH for β-amylase is 4.0–5.0 They belong to glycoside hydrolase family 14.
The substrate spectrum for beta-amylase is:
- Polysaccharides containing alpha-(1-4)-linked D-glucose units + H2O (specific for alpha-(1-4)-linkages, requirements for non-reducing chain end)
- Starch + H2O
- Amylopectin + H2O
- Glycogen
- Amylose + H2O
- Alpha-D-glucopyranosyl-(1-4)-2-deoxy-D-glucal (maltal)
Inhibitors include Glucose, Maltose (competitive), Alpha-methyl-glucoside, Cyclodextrins (e.g. cyclohexaamylose), o-Iodosobenzoate, Ag, Hg, Cu, N-Ethylmaleimide, p-Chloromercuribenzoate (reversed by DTT or mercaptoethanol, reversed by glutathione), Pb, Ni, Cd, Fe, Zn, Mn, Mg, EDTA, Beta-amylase inhibitor (from Streptomyces sp. No. 54), K2PtCl6, K2PtCl4, K2IrCl6, Na2PdCl6, CO3, and Iodoacetamide.