title: Quantitation of soluble and skeletal alkaline phosphatase, and insoluble alkaline phosphatase anchor-hydrolase activities in human serum.
abstract: BACKGROUND
  The current studies were intended to compare the circulating levels of total and anchorless (soluble) skeletal and hepatic ALP isoenzyme activities, and insoluble ALP anchor-hydrolase activity in serum of postmenopausal women.
  
  
  METHODS
  Preliminary studies of the insoluble ALP anchor-hydrolase activity in serum revealed a pH optimum of pH 5-6.5, a sensitivity to inactivation by heat at temperatures >45 degrees C (t(1/2)=8-9 min at 60 degrees C), and an apparent K(M) (at pH 7.5) of 40-45 mU/ml of insoluble skeletal 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 sufficient for the conversion of anchor-intact (insoluble) ALP into the anchorless, soluble form, assuming activation by serum lipids and/or bile salts. Distributions of results for total, skeletal, hepatic, and insoluble ALP anchor-hydrolase activity were skewed toward the higher range and leptokurtotic (p<0.01 for each). Total ALP activity ranged from 42% to 208% of the group mean value; skeletal, hepatic, and insoluble ALP anchor-hydrolase activities 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 group mean value.
  
  
  CONCLUSIONS
  The correlations between the total and both skeletal (r=0.711, p<0.001) and hepatic (r=0.782, p<0.001) ALP isoform activities were predictive. Although correlations were also observed between 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).
authors.affiliation: Jerry L. Pettis Memorial Veterans Medical Center, 11201 Benton Street, Loma Linda, CA 92357, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Anh
authors.forename: A
authors.initials: A
authors.lastname: Eden
authors.forename: J R
authors.initials: JR
authors.lastname: Farley
mesh_terms: D000469:Alkaline Phosphatase / Q000302:isolation & purification / Q000378:metabolism*; D001842:Bone and Bones / Q000201:enzymology*; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008875:Middle Aged; D010739:Phospholipase D / Q000097:blood*; D012995:Solubility
chemical_list: D007527:Isoenzymes; D000469:Alkaline Phosphatase; D010739:Phospholipase D; C065017:glycoprotein phospholipase D