Botulinum toxin is produced by Clostridium botulinum, a gram-negative bacterium. The toxin actually consists of 7 related toxins, types A, B, C1, D, E, F and G. The toxin is synthesized as a protoxin of 150 kDa, which is proteolytically cleaved to a light (L) and heavy (H) chains that remain linked by a disulfide bond. Nerve terminals have receptors for both L and H chains. The L-chain is transported across the nerve terminal membrane by endocytosis. These L chains are metaloproteinases - proteases that require metal ions for activity. The L-chain binds Zn2+, and it proteolytically degrades several proteins that make up the SNARE complex. A) What do you suppose happens when botulinum toxin is injected near the neuromuscular junctions? B) From this conclusion, what do you suppose the basis for botox injections?

A. Botulinum toxin possesses a heavy chain and a light chain, each of which takes part in the toxicity. The binding of the protein and its invasion within a nerve cell is permitted by the heavy chain. After the entry is permitted, the light chain functions like a protease and chops proteins, which would usually permit neurotransmitters to discharge out from the cell. This is basically a commotion of exocytosis or the discharging of neurotransmitters.

The acetylcholine, that is, the obstructed neurotransmitter generally conducts a nerve impulse to a muscle, allowing the muscle to contract. By inhibiting the neurotransmitter, the botulinum toxin results in its distinctive flaccid paralysis.

B. The small doses of the sterile, purified botulinum toxin when used in a medical setting as an injectable form prevent the release of a chemical known as acetylcholine by the nerve cells, which signal contraction of the muscles. By selectively interfering with the underlying tendency of the muscles to contract, the prevailing frown lines are smoothed out, and in the majority of the cases are almost invisible for a week.