The high-Mr isoenzyme of alkaline phosphatase (AP, EC 3.1.3.1), a highly sensitive index to cholestasis, was measured by liquid chromatography in 45 patients with cystic fibrosis. Results of serum tests for liver dysfunction--including gamma-glutamyltransferase, aspartate aminotransferase, alanine aminotransferase, total AP, bilirubin, and bile acids--were compared with those for high-Mr AP. Values for high-Mr AP were increased in 44.4% of our patient population, with activities ranging from 0.4 to 17.3 U/L. The upper limit in the control group was 2.5 U/L. We find increased high-Mr AP to be a more sensitive indicator of liver dysfunction in patients with cystic fibrosis than are other tests.
This simplified HPLC method for measurement of high-molecular-mass alkaline phosphatase (high-Mr AP; EC 3.1.3.1) in serum and bile is rapid (time for column preparation and separation 30 min), reproducible (CV 4.2%), and highly sensitive (detects high-Mr AP in healthy controls at 1-3% of total AP activity in serum), and is suitable for processing small batches of sample. We characterized high-Mr AP in serum and bile by incubating samples with L-phenylalanine, neuraminidase, 1-butanol, or wheat-germ lectin, and by determining stability to heat. High-Mr AP activity was determined in sera of patients with various liver diseases (4-32% of total AP serum activity) and results were compared with those by electrophoresis on agarose.
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