What is Amylase (Alpha-Amylase)?
Amylase is a digestive enzyme that catalyzes the hydrolysis of α-1,4-glucosidic bonds in starch and related carbohydrates, breaking them down into smaller sugars and dextrins. 1
Biochemical Properties and Mechanism
Alpha-amylase functions as a retaining glycosidase, meaning it cleaves starch molecules while maintaining the alpha anomeric configuration of the resulting products 2
The enzyme adopts a (β/α)8-barrel catalytic domain structure and is classified primarily in glycoside hydrolase family GH13, though it also appears in families GH57, GH119, and possibly GH126 1
Alpha-amylase is dextrinogenic and attacks the interior of starch molecules (endohydrolase activity), distinguishing it from beta-amylase which only acts at non-reducing chain ends 3
The enzyme exhibits multiple attack behavior, remaining attached to the substrate after initial cleavage to perform several more cleavages before dissociation 3
Sites of Production and Expression
Amylase is primarily expressed in the pancreas and salivary glands, where it plays its classical role in starch digestion 4
The enzyme is also expressed in human small intestinal epithelial cells (specifically the duodenum at the second-highest mRNA level after pancreas), where it affects cell proliferation and differentiation 4
In intestinal epithelial cells, amylase is detected intracellularly but not secreted into the culture medium, suggesting a distinct intracellular function 4
Amylase requires the presence of the enzyme itself for digestion of raw cornstarch, and this enzyme may not be fully present until 2 years of age in children 5
Clinical Measurement and Significance
Diagnostic Applications
Pleural fluid amylase measurement should be requested if acute pancreatitis or rupture of the esophagus is suspected 5
Pleural fluid amylase levels are considered elevated if they are higher than the upper limits of normal for serum or if the pleural fluid/serum ratio is >1.0 5
Elevated pleural amylase suggests acute pancreatitis, pancreatic pseudocyst, rupture of the esophagus, or pleural malignancy (approximately 10% of malignant effusions have raised pleural amylase levels) 5
Iso-enzyme Analysis
Iso-enzyme analysis is useful in differentiating high amylase levels secondary to malignancy or ruptured oesophagus from those raised in association with abdominal pathology 5
Esophageal rupture shows amylase of salivary origin on iso-enzyme analysis 5, 6
If salivary amylase is raised and oesophageal rupture is not suspected, malignancy is most likely 5
Pleural effusions associated with pancreatic disease usually contain pancreatic amylase 5
Industrial and Therapeutic Applications
Alpha-amylase has extensive industrial applications including starch conversion, food processing, detergent manufacturing, paper and textile industries, and fuel alcohol production 7
In medical therapeutics, pancrelipase (containing lipase, protease, and amylase) has been used in conjunction with cornstarch therapy to reduce gastrointestinal side effects in patients with Glycogen Storage Disease Type I, though routine usage is not recommended 5