Two-site property of thenoyltrifluoroacetone inhibiting succinate-ubiquinone reductase.

It is proved by using the Dixon plot and the Lineweaver-Burk plot that thenoyltrifluoroacetone (TTFA) has two inhibitive sites affecting the reduction of ubiquinone catalyzed by succinate-ubiquinone reductase. The high affinity site (inhibited at the concentration of thenoyltrifluoroacetone less than 20 mumol/L) shows noncompetitive with substrate Q2, while the low affinity site (inhibited at the concentration of TTFA over 20 mumol/L) shows competitive. It is suggested that both the reducing steps of Q----QH-. and QH-.----QH2 are inhibited by thenoyltrifluoroacetone.