Mitochondrial respiratory chain defects are not accompanied by an increasein the activities of lactate dehydrogenase or manganese superoxide dismutase in paediatric skeletal muscle biopsies

Both the activity of lactate dehydrogenase (LDH) and the quantity of mangan ese superoxide dismutase (MnSOD) protein have been reported to be increased in fibroblasts from individuals with mitochondrial electron transport chai n defects. To ascertain whether this is a general phenomenon, we have deter mined the specific activities of these enzymes in skeletal muscle biopsies from control individuals and patients with defined electron transport chain defects. On investigation, both LDH and MnSOD activities were not found to be elevated. These findings suggest a possible fundamental difference betw een skeletal muscle preparations and fibroblasts with regard to their metab olic response to an electron transport chain defect.