Effect of some cardiac and respiratory drugs on succinate-cytochrome c reductase.

Succinate-cytochrome c reductase was inhibited in vitro and in vivo by phenobarbitone, aminophylline and neostigmine using both 2,6-dichlorophenolindophenol (DCIP) and cytochrome c (cyt c) as substrates. The enzyme was also activated by gallamine towards both substrates. In vitro, phenobarbitone and aminophylline inhibited the enzyme with respect to the reduction of DCIP and cyt c in a non-competitive manner with Ki values of 1.5 x 10(-5) and 5.7 x 10(-5)M, respectively. Moreover, neostigmine competitively inhibited the enzyme towards both substrates with Ki values of 1.36 x 10(-5) and 1.50 x 10(-5)M, respectively.