DETERMINATION OF THE ACTIVITIES OF THE ENZYME COMPLEXES OF THE ELECTRON-TRANSPORT CHAIN IN HUMAN FIBROBLASTS

In order to improve the determination of the activities of the enzyme complexes of the electron transport chain (ETC) in fibroblasts, we cha racterized the isolation of mitochondria and measured enzyme activitie s in mitochondrial preparations from fibroblasts of control subjects a nd patients with suspected mitochondrial cytopathy, The isolation proc edure yielded 54% of the citrate synthase activity in fibroblasts, wit h a 6-fold enrichment in this mitochondrial marker enzyme. The activit ies of the complexes of the ETC were linear with time and with the mit ochondrial protein concentration used, The coefficients of variation f or the enzyme activities determined were in the range of 10% in mitoch ondria from identical fibroblast cultures and between 30 and 70% in mi tochondria from different fibroblast cultures of the same or of differ ent patients, Decreased activities of one or more enzyme complexes (de fined as an activity below the 95% confidence limit of control values) were found in 15 of 22 patients investigated. When compared with acti vities obtained in liver or skeletal muscle obtained at autopsy, the r esults were identical in three but different in two patients, The stud ies show that the activities of the enzyme complexes of the ETC can be determined reliably and reproducibly in mitochondria isolated from fi broblasts and that the results obtained are potentially useful for the diagnosis of mitochondrial cytopathies in patients with suggestive sy mptoms and signs.