β-Amylase

β-Amylase

β-amylase (β-amylase), also known as starch β-1,4-maltosidase, is one of amylases, widely present in barley, wheat, sweet potato, soybean and other higher plants and Bacillus Microbes. It is the main saccharification agent for beer brewing and caramel (malt syrup) manufacture. High-malt syrups with a maltose content of 60% to 70% can be produced by saccharifying starch materials that have been acidified or liquefied with α-amylase produced by microorganisms such as Bacillus polymyxa and Bacillus megaterium.

Figure 1. Protein structure of β-Amylase.

Source of β-Amylase

β-amylase is mainly found in higher plants, especially grains, such as barley, wheat, etc., also exists in sweet potatoes, soybeans, but not in animals. The β-amylase currently used in industry mainly includes plant β-amylase and microbial β-amylase.Due to the high production cost of plant-derived β-amylase, people have begun to attach importance to microbial-derived β-amylase. Since the 1960s, it has been found that Bacillus megaterium and Polymyxa. Bacteria and Bacillus cereus β-amylase, but their heat resistance is lower than plant β-amylase.

Properties

The active center of β-amylase contains a sulfhydryl group (-SH), therefore, some oxidants, heavy metal ions and sulfhydryl reagents can inactivate it, while reducing glutathione and cysteine have a protective effect. The optimal pH range of β-amylase and α-amylase are basically the same, generally around 5.0 ~ 6.5, but the stability of β-amylase is significantly lower than that of α-amylase, and generally will be inactivated above 70 ℃. The stability of β-amylase from different sources also varies greatly. The optimum temperature for soybean β-amylase is about 60 ℃, the optimum temperature for barley β-amylase is 50 ~ 55 ℃, and the most suitable for bacterial β-amylase. Suitable temperature is generally lower than 50 ℃.

Functions

β-amylase is an exo-amylase, which cuts the separated α-1,4 bonds from non-reducing ends when acting on starch, and the hydrolysate is all maltose. Because the amylase changes the configuration of C1 in the hydrolysate maltose molecule from alpha type to beta type during the hydrolysis process, it is called beta-amylase. β-amylase cannot hydrolyze the α-1,6 bond of amylopectin, nor can it continue to hydrolyze across branch points, so hydrolysis of amylopectin is incomplete, leaving large-molecule β-limit dextrins. When β-amylase hydrolyzes amylose, if the starch molecule consists of an even number of glucose units, the final hydrolysate is all maltose; if the starch molecule consists of an odd number of glucose units, the final hydrolysate contains a small amount of glucose in addition to maltose. When β-amylase hydrolyzes starch, since there are always macromolecules starting from the end of the molecule, the viscosity decreases slowly and cannot be used as a liquefaction enzyme, while β-amylase hydrolyzes starch hydrolysates such as maltodextrin and malto-oligosaccharide At the time, the hydrolysis rate is very fast, so it is used as a saccharification enzyme.

Acute pancreatitis

Increased serum amylase is more common in acute pancreatitis, it is one of the important diagnostic indicators of acute pancreatitis. Activity begins to increase 6 to 12 hours after onset, peaks at 24 hours, begins to decrease at 48 hours, and returns to normal after 3 to 5 days. Although the degree of increase in amylase activity is not necessarily related to the degree of pancreatic injury, the greater the degree of increase, the greater the possibility of acute pancreatitis, so although amylase is still used as a diagnosis of acute pancreatitis The index is preferred, but its specificity and sensitivity are not high enough. When acute pancreatitis is suspected, the patient's serum and urine amylase activities should be continuously and dynamically observed, and combined with clinical conditions and other tests, such as pancreatic lipase, trypsin and other measurements, to make a diagnosis.

Figure 2. Acute pancreatitis.