<prompt> Barbiturates act on which step of mitochondrial respiratory chain?Compelx 1 to co-enzyme QCompelx 2 to co-enzyme QCo-enzyme Q to compelx 3Cytochrome C to compelx 4  <response>: 1. Complex I to Co-Q specific inhibitorsAlkylguanides guanethidine, hypotensive drugRotenone, insecticide and fish poisonBarbiturates amobarbital, sedativeChlorpromazine, tranquilizerPiericidin, antibioticRef: DM Vasudevan Textbook of Medical Biochemistry, 6th edition, page no: 234 