Cyanide affects respiratory chain by ?

Ans. is 'd' i.e., Non-competitive irreversible inhibition Cyanide inhibits cytochrome oxidase (respiratory chain) irreversibly, and non-competitively. Types of enzyme inhibition Enzyme inhibition is of two types :? Reversible and Irreversible Reversible inhibition Reversible inhibition may be of following types :? i) Competitive inhibition (substrate analogue inhibition) The inhibitor competes with substrate for catalytic (substrate-binding) site of enzyme. Inhibitor resembles substrate in structural configuration. Inhibition can be reversed by increasing the concentration of substrate. Competitive inhibition increases km of the enzyme but Vmax does not change. Examples of competitive inhibition are inhibition of succinate dehydrogenase by malonate, HMG CoA reductase by statins, carbonic anhydrase by acetazolamide and LDH by oxamate. ii) Non-competitive inhibition Inhibitor binds at a site other than the substrate-binding site. Thus inhibitor can bind to both free enzyme and enzyme substrate complex. The inhibitor therefore lowers the concentration of active enzyme. A non-competitive inhibitor cause decrease in Vmax but no change in Km. Inhibition can be reversed only by exhaustive dialysis of inhibited enzyme.