Catalytic properties of mitochondrial NADH-ubiquinone reductase (Complex I)

Qualitative and quantitative characteristics of the reactions catalyzed by the most complex and least understood proton translocating unit of the mamm alian respiratory chain (NADH-ubiquinone oxidoreductase, Complex I) are des cribed for enzyme preparations differing in degree of resolution-from intac t mitochondria to homogeneous small enzyme fragments. Special attention is given to the problems and pitfalls of reliable interpretation of the kineti c analysis of the enzyme activities. Detailed analysis of the problems conc erning the slow active/inactive reversible enzyme transition is provided.