This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
Diphtheria toxin acts by 
Select and explain. 
A. Inhibiting acetyl choline release, B. Inhibiting glucose transpo, C. Inhibiting levels of cyclic AMP, D. Inhibiting protein synthesis
D: Inhibiting protein synthesis
Answer: D: Inhibiting protein synthesis 
Explanation: The diphtheria toxin acts by inhibiting protein synthesis. Specifically, a fragment B heparin binding and fragment A inhibits polypeptide chain elongation in the presence of nicotinamide adenine dinucleotide by inactivating the elongation factor EF-2. It has a special affinity for ceain tissues such as the myocardium, adrenals and nerve endings. Reference: Textbook of Microbiology; Anathanarayan and panicker's; 10th edition; Page no: 240