The second coenzyme Q1 binding site of bovine heart NADH:: Coenzyme Q oxidoreductase

The rotenone sensitivity of bovine heart NADH: coenzyme Q oxidoreductase (Complex 1) depends significantly on coenzyme Q(1) concentration. The rotenone-insensitive Complex I reaction in Q(1) concentration range above 300 muM indicates an ordered sequential mechanism with Q(1) and reduced Q(1) (Q(1)H(2)) as the initial substrate to bind to the enzyme and the last product to be released from the enzyme product complex, respectively. This is the case in the rotenone-sensitive reaction although both K-m and V-max values of the rotenone-insensitive reaction for Q(1) are significantly higher than those of the rotenone-sensitive reaction (Nakashinia et al., 2002, J. Bioenerg. Biomemb. 34, 11-19). This rigorous control mechanism between the nucleotide and ubiquinone binding sites strongly suggests that the rotenone-insensitive reaction is also physiologically relevant.