Cyanide affects respiratory chain by

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