DIFFERENCES BETWEEN THE SUGAR MOIETIES OF LIVER-TYPE AND BONE-TYPE ALKALINE-PHOSPHATASES - A REEVALUATION

We re-evaluated the differences between the sugar moieties of liver an d bone alkaline phosphatases (ALPs). Sialic acid was added to ALP suga r moieties by alpha 2,3- or 2,6-sialyltransferase treatment of the asi alo-form ALP (neuraminidase-treated ALP). Asialo-bone ALP was converte d to a liver-like ALP by the 2,6-sialyltransferase treatment. The resu lting liver-like ALP was less susceptible to neuraminidase than non-tr eated bone ALP, but was still labile to heat exposure at 56 degrees C like non-treated bone ALP. However, after the O-linked sugar moiety ha d been released by additional treatment with O-glycanase the liver-lik e ALP became more heat stable at 56 degrees C, like non-treated liver ALP. Non-treated liver ALP reacted specifically with anti-liver ALP mo noclonal antibody, and non-treated bone ALP reacted with both anti-liv er and anti-bone ALP antibodies. The asialo-bone ALP still reacted wit h anti-bone ALP antibody, whereas the asialo-form liver ALP showed lit tle, if any, reaction with anti-liver and anti-bone ALP antibodies. Ne uraminidase and O-glycanase-treated bone ALP reacted less with anti-bo ne ALP antibody. After O-glycanase treatment, bone ALP molecules depri ved of an O-linked sugar moiety had a molecular size and heat stabilit y similar to liver ALP. The difference between liver and bone ALP mole cules may be due not only to their manner of sialic acid linkage but a lso to the attachment of the O-linked sugar moiety.