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 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).
Anh
D J
DJ
Jerry L. Pettis Memorial Veterans Medical Center, 11201 Benton Street, Loma Linda, CA 92357, USA.
Eden
A
A
Farley
J R
JR
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
D007527:Isoenzymes; D000469:Alkaline Phosphatase; D010739:Phospholipase D; C065017:glycoprotein phospholipase D