Complex sentence: Many of these toxins are polypeptides (e.g. α-bungarotoxin from cobras), but non-peptide toxins such as tetrodotoxin from the puffer fish are also extremely potent.
Split into simpler sentences: Many of these toxins are polypeptides (e.g. α-bungarotoxin from cobras). However, non-peptide toxins such as tetrodotoxin from the puffer fish are also extremely potent.