Regan isoenzyme

Alkaline phosphatase catalyzes the biochemical splitting of phosphoric acid ester. AP (W.M. Roberts, 1933) is found in the liver, bone, kidney, intestine, lung and placenta. A Regan isoenzyme can be detected as an ectopic variation of placental AP in tumour patients (10-30% of cases). The AP of the liver is located in the cytoplasm and in the membranes, primarily at the biliary pole. Placental AP is also present in the liver. The AP of bile duct epithelia is not elevated in healthy individuals. The serum activity of AP is predominantly due to the isoenzymes of the liver and osteoblasts only 14% are of renal origin. Half-life is 3-7 days. 

In 1968, Fishman and his collaborators reported the identification of an ALP in the serum of a patient with metastatic squamous cell carcinoma of the lung that was biochemicaEy and immunologicaUy identical with the ALP of a normal placenta. The newly discovered isoenzyme was termed the Regan isoenzyme after the patient in whom it was discovered. The Regan isoenzyme has been detected in tumor tissues and in sera of patients with many types of malignant disease and in some patients with nonmalignant diseases. An incidence of the isoenzyme of 3% to 15% in sera of cancer patients has been estimated, but this varies with the sensitivity of the methods used for its detection. Other variant forms of ALP have since been discovered in tumor tissues. These variants show many similarities to normal placental ALP but may differ in other properties, such as response to certain inhibitors. 

A result of the application of the techniques of isoenzyme analysis to the characterization of ALP in serum was the discovery that forms of the enzyme essentially identical with the normal placental isoenzyme appear in the sera of some patients with malignant diseases. These carcinopla-cental isoenzymes (e.g., Regan isoenzyme) appear to result from the derepression of the placental ALP gene. As described below, the presence of these isoenzymes can be readily detected in serum by their stability at 65 °C. Tumors have also been found to produce ALPs that appear to be modified forms of nonplacental isoenzymes (Kasahara isoenzyme). 

Nl. Nathanson, L., and Fishman, W. H., New observations on the Regan isoenzyme of alkaline phosphatase in cancer patients. Cancer 27, 1388-1397 (1971). 

A group of enzymes which hydrolyse phosphate esters at optimal pHs of about 10. Alkaline phosphatase isoenzymes occur in many organs including intestine, bone (particularly osteoblasts), placenta, and liver and are also found in some patients with cancer (Regan isoenzyme). 

A heat stable alkaline phosphatase isoenzyme similar to placental isoenzyme. It is found in some patients with carcinoma. Regan isoenzyme is named after the first patient in whom it was found. 

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