**Question:** All are true regarding diphtheria toxin EXCEPT:

A. Diphtheria toxin is a protein produced by the bacterium Corynebacterium diphtheriae.
B. Diphtheria toxin causes paralysis by binding to nicotinic acetylcholine receptors.
C. Diphtheria toxin is a glycoprotein that interferes with protein synthesis.
D. Diphtheria toxin is an enzyme that breaks down ATP.

**Core Concept:**
Diphtheria is a bacterial infection caused by Corynebacterium diphtheriae. The primary toxin produced by this bacterium is diphtheria toxin (DT), which is a glycoprotein. DT has multiple effects on the host, including interference with protein synthesis, inhibition of adenyl cyclase, and activation of protein kinase C.

**Why the Correct Answer is Right:**
Diphtheria toxin (DT) is a glycoprotein that interferes with protein synthesis. It does not act as an enzyme and break down ATP (Option D), nor does it directly cause paralysis by binding to nicotinic acetylcholine receptors (Option B). However, Option C is partially correct as DT does interfere with protein synthesis, but the explanation for the correct answer is more specific and detailed.

**Why Each Wrong Option is Incorrect:**
Option A is incorrect as diphtheria toxin is a protein, not a bacterial species. Diphtheria toxin causes paralysis by inhibiting protein synthesis, not by binding to nicotinic acetylcholine receptors (Option B). Diphtheria toxin is a glycoprotein (Option C), which does interfere with protein synthesis. Diphtheria toxin is an enzyme that breaks down ATP (Option D), but it does not specifically target ATP.

**Clinical Pearl:**
Diphtheria is a serious infectious disease that primarily affects the respiratory system. Its primary toxin, diphtheria toxin, is a crucial target for vaccination against diphtheria. Understanding the mechanism of action of diphtheria toxin is essential for understanding the rationale behind vaccination strategies in preventing diphtheria.