Review Article

Alkaline Phosphatase-Biochemistry, Biological Functions Measurement and Clinical Relevance

Elena Miriouni^1,2, Ioulia Trifonidi^1,2, Efstathios Chronopoulos², Konstantinos Makris^1,2

1. Clinical Biochemistry Department, KAT General Hospital, Kifissia, Athens, Greece
2. Laboratory for the Research of Musculoskeletal System “Th. Garofalidis”, School of Medicine, National and Kapodistrian, University of Athens, Athens, Greece

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Keywords: Bone ALP, Hypophosphatasia, Paget disease, Tissue-nonspecific ALP, Total ALP

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Abstract

A class of isoenzymes known as alkaline phosphatases (ALPs) is mainly found on the cell membrane’s outer layer. Their main function is to catalyze the hydrolysis of organic phosphate esters present in the extracellular space. Zinc and magnesium serve as important co-factors for this enzyme. ALPs have distinct physiochemical features and are real isoenzymes, catalyzing similar processes. ALP is cytosolic in the liver and can be found in hepatocyte canalicular membranes. ALPs are also found in other organs (placenta, ileal mucosa, kidney, and bone). The majority of ALP concentration in serum (>80%) is derived from the liver and bone, with lower quantities from the intestines. While ALPs play a crucial role in processes such as phosphate metabolism and bone mineralization, the exact physiological function of ALPs remains largely unknown. Further research is necessary to fully understand their functions and regulatory mechanisms across different tissues.

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