Quantitation of soluble and skeletal alkaline phosphatase, and insoluble alkaline phosphatase anchor-hydrolase activities in human serum

Background: The current studies were intended to compare the circulating le vels of total and anchorless (soluble) skeletal and hepatic ALP isoenzyme a ctivities, and insoluble ALP anchor- hydrolase activity in serum of postmen opausal women. Methods: Preliminary studies of the insoluble ALP anchor-hyd rolase activity in serum revealed a pH Optimum of pH 5-6.5, a sensitivity t o inactivation by heat at temperatures > 45 degreesC (t(1/2) = 8-9 min at 6 0 degreesC) and an apparent K-M (at pH 7.5) of 40-45 mU/ml of insoluble ske letal ALP activity. Results: Serum analyses showed that 94.5 +/- 0.5% (mean SEM) of the ALP activity in serum was in the anchorless, soluble form. The data were also consistent with the notion that the amount of insoluble ALP anchor- hydrolase activity in serum, 52.8 +/- 0.8 U/l (mean SEM), was suff icient for the conversion of anchor-intact (insoluble) ALP into the anchorl ess, soluble form, assuming activation by serum lipids and/or bile salts. D istributions of results for total. skeletal, hepatic, and insoluble ALP anc hor-hydrolase activity were skewed toward the higher range and leptokurtoti c (p < 0.01 for each). Total ALP activity ranged from 42% to 208% of the gr oup mean value: skeletal, hepatic, and insoluble ALP anchor-hydrolase activ ities ranged from 5% to 306%, 33% to 277%, and 2% to 325%, respectively. In contrast. the soluble ALP fraction only ranged from 71% to 106% of the gro up mean value. Conclusions: The correlations between the total and both ske letal (r = 0.711, p < 0.001) and hepatic (r = 0.782, p < 0,001) ALP isoform activities were predictive. Although correlations were also observed betwe en insoluble ALP anchor-hydrolase activity and total (r = 0.197, p < 0.001) , hepatic (r = 0,184, p < 0.001) and skeletal ALP activities (r = 0.118, p < 0.05), those relationships were not predictive (r(2) < 0.04). (C) 2001 El sevier Science B.V. All rights reserved.