Mevalonate Kinase in Lysates of Cultured Human Fibroblasts and Lymphoblasts: Kinetic Properties, Assay Conditions, Carrier Detection and Measurement of Residual Activity in a Patient with Mevalonic Aciduria

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Abstract
An assay has been developed for the measurement of mevalonate kinase activity in extracts of cultured human fibroblasts and lymphoblasts. Individual elements of the assay were investigated in order to achieve optimum conditions. Apparent Michaelis constants (K(M)app) for the substrates mevalonic acid and adenosine-5'-triphosphate were 22 ± 10 μmol/l and 0.42-0.53 mmol/1, respectively, in lysates of control fibroblast lines. The same values in lysates of a control lymphoblast line were 17 μmol/l and 0.23 mmol/1, respectively. Mevalonate kinase activity in extracts of cultured fibroblasts derived from 6 control individuals was 3.24 ± (SD) 0.91 nmol/min/mg protein. The activity in extracts of fibroblasts derived from a patient with mevalonic aciduria was 0.15 ± 0.10 nmol/min/mg protein, approximately 5 % of the control mean. The parents and brother of the patient displayed mevalonate kinase activities in fibroblast extracts approximating 38-42% of the control mean. Substantially higher mevalonate kinase activity was documented in extracts of cultured lymphoblasts. When assayed on various occasions, the mean activity of mevalonate kinase in extracts of lymphoblasts derived from the parents, brother and maternal grandmother of the patient ranged from 27 to 32% of the mean activity of 9.8 ± (SD)