The effect of neuraminidase on the molecular weight and the isoelectric point of the steroid induced alkaline phosphatase of dogs.

Isoelectric focusing and gradient polyacrylamide gel electrophoresis were used to define the physical differences between canine liver alkaline phosphatase (LAP) and steroid induced alkaline phosphatase (SIAP). LAP has an isoelectric point (pI) of pH 4.3 and a molecular radius (Mr) of 100,000, while SIAP has a pI of pH 3.5 and an Mr of 110,000. After removal of sialic acid residues by neuraminidase, the two isoenzymes were still distinct. The pIs of both LAP and SIAP were increased with the pI of LAP becoming pH 4.7 to 4.8 and that of SIAP becoming pH 4.5 to 4.6. On gradient polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate, SIAP gave a single band of Mr 100 000 after neuraminidase treatment, while LAP increased in molecular size in spite of the denaturing conditions of the electrophoretic separation.