Complex I of respiratory chain is inhibited by

* Site I: This involves the transfer of electrons from NADH-CoQ. Obviously, this step is omitted by succinic dehydrogenase whose FADH2 prosthetic group transfers its electrons directly to CoQ bypassing NADH. This step is blocked by piericidin, rotenone, amobarbital, ceain drugs like chlorpromazine, guanethidine. Site-I (Complex-I) * Rotenone: A fish poison and also insecticide. Inhibits transfer of electrons through complex-I-NADH-Q-reductase. * Amobarbital (Amytal) and Secobarbital: Inhibits electron transfer through NADH-Q reductase. * Piericidin A: An antibiotic. Blocks electron transfer by competing with CoQ. * Drugs: Chlorpromazine and hypotensive drug like guanethidine.Ref: MN Chatterjea Textbook of Medical Biochemistry, 8th edition, page no: 143