POSTTRANSLATIONAL HETEROGENEITY OF BONE ALKALINE-PHOSPHATASE IN METABOLIC BONE-DISEASE

Bone alkaline phosphatase is a marker of osteoblast activity. In order to study the posttranscriptional modification (glycosylation) of bone alkaline phosphatase in bone disease, we investigated the relationshi p between mass and catalytic activity of bone alkaline phosphatase in patients with osteoporosis and hyperthyroidism, Serum bone alkaline ph osphatase activity was measured after lectin precipitation using the I so-ALP test kit. Mass concentration of bone alkaline phosphatase was d etermined with an immunoradiometric assay (Tandem-R Ostase). In genera l, serum bone alkaline phosphatase mass and activity concentration cor related well. The activity : mass ratio of bone alkaline phosphatase w as low in hyperthyroidism. Activation energy of the reaction catalysed by bone alkaline phosphatase was high in osteoporosis and in hyperthy roidism. Experiments with neuraminidase digestion further demonstrated that the thermodynamic heterogeneity of bone alkaline phosphatase can be explained by a different glycosylation of the enzyme.