Table 2.

Respiratory chain enzymes and mitochondrial DNA levels

	Patient 1	Patient 2	Patient 3	Patient 4	Patient 5	Normal range
Complex I	17	29	4	38	42	82–118
Complex II	119	99	170	154	200	89–120
Complex III	67	97	22	36	30	68–136
Complex IV	73	103	36	20	63	63–123
Citrate synthase	126	292	297	303	254	93–111
mtDNA/nDNA	61	53	6	130	7	66–146
Enzyme defect	I	I	I, III, IV	I, III, IV	I, III, IV

Enzyme activities are expressed as % of control mean relative to protein. Complex I is NADH-Coenzyme Q1 oxidoreductase; Complex II is Succinate-Coenzyme Q1 oxidoreductase; Complex III is decylbenzylquinol-cytochrome c oxidoreductase; Complex IV is cytochrome c oxidase. mtDNA/nDNA is the ratio of mitochondrial DNA relative to nuclear DNA expressed as % of control mean. ‘Normal Range’ was determined on at least six tissue samples obtained from children lacking evidence of respiratory chain disease. Methods for enzyme and DNA analyses were as described previously (Dimmock et al. 2008; Tzoulis et al. 2006)