Search

We developed an assay method for pyruvate dehydrogenase phosphatase activity using [1-14C]pyruvate and measured pyruvate dehydrogenase phosphatase activity in cultured skin fibroblasts from three patients with congenital lactic acidemia due to a defect in activation of the pyruvate dehydrogenase complex. The enzyme activity of their fibroblasts was significantly reduced to 50.7%, 64.6% and 63.1% of that of control fibroblasts. These observations suggest that the defect in activation of the pyruvate dehydrogenase complex in these patients might be due to a reduction in pyruvate dehydrogenase phosphatase activity.

We assayed the rates of lactate production from [1-14C]pyruvate and decarboxylation of [1-14C]pyruvate in cultured skin fibroblasts from 8 patients with disorders of pyruvate metabolism and 16 control subjects. The disorders of pyruvate metabolism could be more readily detected by measuring the ratio between the rates of lactate production and pyruvate decarboxylation by cultured skin fibroblasts than by measuring either the rate in isolation.

The interactions of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]with phytohemagglutinin (PHA)-stimulated lymphocytes from normal subjects and three patients with vitamin D-dependent rickets (DDR) type II were investigated. Impaired nuclear uptake and normal cytosol binding of [3H]1,25-(OH)2D3 were observed with PHA-stimulated lymphocytes of these patients as with their cultured skin fibroblasts. Furthermore, the incorporation of [14C]thymidine into PHA-stimulated lymphocytes of the patients was not reduced by 1,25-(OH)2D3, which is known to inhibit proliferation of various cells. These findings suggest that 1,25-(OH)2D3 receptors are reduced or absent in patients with DDR type II. Thus, the capacities of cytosol binding and nuclear uptake of 1,25-(OH)2D3 in PHA-stimulated lymphocytes seem to reflect those of endo-organs such as the intestine and bone. These findings show that a test of the effect of 1,25-(OH)2D3 on thymidine incorporation into PHA-stimulated lymphocytes is useful for rapid diagnosis of DDR type II.