This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Enzymes, Subject name: Biochemistry
Cyanide affects respiratory chain by 
Select and explain. 
A. Non-competitive reversible inhibition, B. Competitive reversible inhibition, C. Suicide irreversible inhibition, D. Non-competitive irreversible inhibition
D: Non-competitive irreversible inhibition
Answer: D: Non-competitive irreversible inhibition 
Explanation: The toxicity of cyanide is due to its inhibitory effect on the terminal cytochrome which brings cellular respiration to a standstill. The inhibitor usually binds to a different domain on the enzyme, other than the substrate binding site. Since these inhibitors have no structural resemblance to the substrate, an increase in the substrate concentration generally does not relieve this inhibition.Ref: DM Vasudevan, Page no: 234