Receptor for diphtheria toxin lies at ?
Cell membrane
Mucous membrane
Nucleus
None
Ans. is 'a' i.e., Cell membrane Diphtheria toxin The diphtheria toxin acts by inhibiting protein synthesis. It inhibits polypeptide chain elongation in the presence of nicotinamide adinine dinucleotide (NAD) by inactivating elongation factor, EF - 2. The diphtheria toxin is a protein which consists of two fragments, A and B. Both fragments are necessary for the toxic effect : Fragment A - has enzymatic activity and inhibits protein synthesis by inhibiting the chain elongation by inactivating the elongation factor - 2 (Ef - 2). Fragment B - responsible for binding the toxin to the cells. The toxin binds to specific receptors (HB-EGF receptors) present on susceptible cells and enters by receptor-mediated endocytosis. Toxin has special affinity for ceain tissues such as myocardium, adrenals and nerve endings.