Alpha Amylase

EC 3.2.1.1

Alpha amylase is an oligosaccharide endoglycosidase, an enzyme that cleaves an internal glycosidic bond within a poly or oligosaccharide. In the case of alpha amylase, it is the 1,4 linkage between two glucose moieties, cleaving the C-O bond between the C1 carbon and the oxygen, although which 1,4 linkage is cleaved is random¹:

Alpha amylase requires calcium for activity, although complete activity only occurs in the presence of certain anions such as Cl-, Phosphate and others². Although many tissues can produce alpha amylase³, the forms found in serum are most often from the pancreas and salivary glands². Several isoenzymes have been detected and characterized from these tissue sources^4,5,6. Alpha amylases can be found in a variety of body fluids and they are some of the few enzymes that can be found in urine from healthy individuals⁷. The main purpose in testing amylase, especially when the appropriate symptoms are present, is to diagnose pancreatitis and other primary and secondary pancreatic pathologies. This can be made more specific by testing for amylase isoenzymes specific to the pancreas^6,8,9. However total amylase is still a very valuable diagnostic tool.

There is some evidence to suggest that lipase might be a superior indicator of pancreatitis^6,10. In practice, both enzymes are often measured. Amylase may also play a role in diagnosing cancers other than pancreatic cancer, such as multiple myeloma and ovarian cancer, although it appears that at least in some of these cases the salivary form may be the more important form of amylase^11,12,13.

Due to the non-specific nature of amylase, many substrates can be used and in the past this often resulted in considerable variability in measuring amylase, depending on which type of reagent was used. As a response, large substrates such as starch have been replaced with smaller, more consistent oligosaccharides². Although no useful spectrophotometric changes occur during the amylase catalyzed hydrolysis of these glycosidic bonds, the release of glucose can be coupled to an enzyme such as hexokinase. This uses ATP to phosphorylate glucose to produce glucose-6-phosphate (G6P). This product can then be coupled to the enzyme glucose-6-phosphate dehydrogenase which uses NAD+ to oxidize G6P. The conversion of NAD+ to NADH can be monitored at 340 nm.

REFERENCES

1. 1. Walsh, C.: Enzymatic Reaction Mechanisms, W.H. Freeman and Company, 1979.
2. 2. Burtis, C.A., Ashwood, E.R. and Bruns, E.R. Tietz Textbook of Clinical Chemistry, W.B. Saunders Company, 2006.
3. 3. Merrit, A.D. and Karn, R.C. The Human Alpha-Amylase Advances in Human Genetics, 8, 135-235, 1977.
4. 4. Skude, G. and Skude, G. Clinical Chemistry: Electrophoretic Separation, Detection and Variation of Amylase Isoenzymes. Scandinavian Journal of Clinical and Laboratory Investigation, 35, 41-47, 1975.
5. 5. Kauffman, D.L., et. al. The Isoenzymes of Parotid Amylase. Archives of Biochemistry and Biophysics, 137, 325-339, 1970.
6. 6. ott, J.A. and Lu, C.J. Lipase Isoforms and Amylase Isoenzymes: Assays and Applications in the Diagnosis of Acute Pancreatitis. Clinical Chemistry, 37, 361-368, 1991.
7. 7. Aw, S.E., et. al. Urinary Isoamylases in the Diagnosis of Chronic Pancreatitis. Gut, 8, 402-407, 1967.
8. 8. Leclerc, P. and Forest, J.C. Variations in Amylase Isoenzymes and Lipase during Acute Pancreatitis, and in Other Disorders Causing Hyperamylasemia.
9. 9. Moridani, M.Y. and Bromberg, I.L. Lipase and Pancreatic Amylase versus Total Amylase as Biomarkers of Pancreatitis: An Analytical Investigation. Clinical Biochemistry, 36, 31-33, 2003.
10. 10. Al-Bahrani, A.Z. and Ammori, B.J. Clinical Laboratory Assessment of Acute Pancreatitis. Clinica Chimica Acta, 362, 26-48, 2005.
11. 11. Motiyama, T. Sialyl Salivary-Type Amylase Associated with Ovarian Cancer. Clinica Chimica Acta, 391, 106-111, 2008.
12. 12. Calvo-Villas, J.M., et. al. Paraneoplastic Hyperamylasaemia in Association with Multiple Myeloma. Acta Haematologica, 117, 242-245, 2007.
13. 13. Pinelli, M., et. al. Amylase: A Disease Activity Index in Multiple Myeloma? Leukemia and Lymphoma, 47, 151-154, 2006.