Isoelectric focusing of neuraminidase-treated alkaline phosphatase isoenzymes on agarose gel.

We attempted to separate bone and liver alkaline phosphatase (EC 3.1.3.1) isoenzymes in human serum by isoelectric focusing on agarose gel. We found that in a pH 3-10 gradient the liver and bone isoenzymes focused into so many bands over a narrow pH range such that the information could not be quantified. However, when the bone isoenzyme in serum was first desialylated at 37 degrees C for a minimum of 6 h, catalyzed by neuraminidase (EC 3.2.1.18) at pH 5.8-6.0, we could detect four distinct bands with pls of 6.7, 6.8, 6.9, and 7.0. Under the same conditions, the liver isoenzyme in human serum focused into one band at pH 7.0. The multiple banding we observed for the desialylated bone isoenzyme has not been previously reported. The method is suited as a qualitative technique for detecting the bone alkaline phosphatase isoenzyme in serum.