* To whom correspondence should be addressed.
Received July 15, 1998
Qualitative and quantitative characteristics of the reactions catalyzed by the most complex and least understood proton translocating unit of the mammalian respiratory chain (NADH-ubiquinone oxidoreductase, Complex I) are described for enzyme preparations differing in degree of resolution--from intact mitochondria to homogeneous small enzyme fragments. Special attention is given to the problems and pitfalls of reliable interpretation of the kinetic analysis of the enzyme activities. Detailed analysis of the problems concerning the slow active/inactive reversible enzyme transition is provided.
KEY WORDS: NADH-ubiquinone reductase, Complex I, respiratory chain, enzyme hysteresis, bovine heart mitochondria