Amylase is an enzyme that plays a central role in breaking down complex carbohydrates. Its primary function is the hydrolysis of starch, a major energy storage molecule found in plants. Amylase is produced by plants, fungi, and bacteria, making it ubiquitous in natural and industrial processes. The enzyme’s ability to degrade starch into simpler sugars is important in fields ranging from human health to applied microbiology.
Classification and Sources of Amylase
Amylases are generally grouped into three main categories, distinguished by how they interact with the starch molecule. Alpha-amylase is the most widespread form, found in humans, animals, plants, and microorganisms. This enzyme acts as an endo-amylase, randomly cleaving the \(\alpha\)-1,4 glycosidic bonds within the starch polymer chain. This action results in the rapid reduction of the molecule’s size.
The main sources of alpha-amylase in humans are the salivary glands and the pancreas, where the enzyme initiates and continues the digestive process. Beta-amylase is primarily found in plants, particularly in seeds, and in certain microbes. This type of amylase acts as an exo-amylase, systematically cleaving maltose units from the non-reducing ends of the starch chain.
Gamma-amylase, also known as glucoamylase, is present in both plants and animals. It works from the non-reducing end of the chain, breaking the \(\alpha\)-1,4 glycosidic bonds and hydrolyzing the \(\alpha\)-1,6 branch points found in starch. This comprehensive action yields individual glucose molecules.
The Chemical Process of Starch Hydrolysis
Starch, the substrate for amylase, is a polysaccharide composed of two main polymer types: amylose and amylopectin. Amylose is a linear chain of glucose units linked by \(\alpha\)-1,4 glycosidic bonds. Amylopectin is a highly branched structure containing both \(\alpha\)-1,4 linkages and \(\alpha\)-1,6 linkages at the branch points.
The catalytic action of amylase involves hydrolysis, a chemical reaction where a water molecule is added across the glycosidic bond. This breaks the bond, separating the glucose units from the larger starch molecule. The specific products depend on the type of amylase acting on the starch.
Alpha-amylase produces a mixture of smaller polysaccharides called dextrins, along with the disaccharide maltose and the trisaccharide maltotriose. Beta-amylase cleaves off only maltose. Gamma-amylase, with its ability to target both types of bonds, yields only glucose as its end product.
Amylase in Human Health and Diagnostics
In the human body, the digestion of starch begins in the mouth with the action of salivary amylase, sometimes referred to as ptyalin. This enzyme starts the conversion of starch into smaller sugars while food is being chewed, which is why starchy foods can begin to taste sweet. The process is then completed in the small intestine by pancreatic amylase, which is secreted into the duodenum.
The physiological presence of amylase in the bloodstream is normally low, but serum levels can rise sharply when certain organs are damaged. Measuring the level of amylase in the blood is a standard diagnostic test, particularly when acute pancreatitis is suspected. Acute pancreatitis, an inflammation of the pancreas, causes the enzyme to leak into the circulation.
A serum amylase level elevated to at least three times the upper limit of normal is considered supportive of an acute pancreatitis diagnosis. However, the diagnostic utility of amylase is time-sensitive; its levels rise quickly but often return to normal within three to seven days. Furthermore, elevated amylase can occur in non-pancreatic conditions, such as kidney disease or salivary gland issues.
Applied Microbiology and Industrial Uses
Microorganisms are a dominant source for the commercial production of amylases due to their rapid growth and the ease with which their enzymes can be manipulated. In the microbiology laboratory, the presence of amylase is often identified using the starch hydrolysis test. Bacteria are grown on a starch-containing agar plate, and after incubation, the plate is flooded with an iodine solution.
Iodine reacts with any residual starch to produce a dark blue-black color. If the bacteria have produced and secreted amylase, a clear zone, or halo, will surround the bacterial growth where the starch has been broken down. This clear zone indicates a positive test for the production of the exoenzyme amylase.
Microbial amylases are among the most important industrial enzymes, accounting for a significant portion of the global enzyme market.
Industrial Applications
In the food industry, these enzymes are used extensively in brewing to break down grain starches into fermentable sugars for yeast. They are also used to produce sweeteners like high-fructose corn syrup and in baking to improve dough texture and loaf volume.
Amylases have also found non-food applications in various manufacturing sectors. In the textile industry, they are used for desizing, which removes the starch-based sizing agents applied to warp threads to prevent breakage during weaving. Highly stable microbial amylases are incorporated into laundry detergents, where they break down tough starch-based stains.