Purified
Human
Proteins

Alkaline Phosphatase (ALP)

EC 3.1.3.1

Alkaline phosphatase (ALP) is a ubiquitous enzyme found in almost every tissue in the body. ALP has a variety of physiological roles as well as functional applications. ALP is a non-specific enzyme which catalyzes the hydrolysis of a wide range of phosphate esters.

Independent of ALP’s roles in clinical diagnostics, alkaline phosphatase is one of the most common enzymes used in chromogenic assays. This is due to a very convenient substrate (p-nitrophenylphosphate) that is essentially colorless, but when the phosphate ester is hydrolyzed by ALP, the bright yellow p-nitrophenylate is formed:

Even though ALP can be found in nearly every tissue in the body, the most clinically relevant forms come from liver, bone, intestine and placenta¹. The predominant form of ALP in the serum of healthy adults is from liver, the next most predominant form is from bone². Therefore the elevation of the liver form of alkaline phosphatase is often due to liver pathologies, and likewise elevation of the bone form often indicates a bone pathology such as Paget’s disease³. However, elevated ALP can be due to non-specific causes and does not always indicate serious disease⁴. Nevertheless alkaline phosphatase is a very useful serum marker, with wide applications from diagnosing hepatoma⁵ to predicting mortality in dialysis patients⁶.