Onions contain also the relatively
rare amino acids S-meth and S-prop (en)ylcysteine sufoxides
(SMCO). It is widely agreed that n-propyl disulphide
is the principal toxin that reduces the activity of glucose-
6-phosphate dehydrogenase in red blood cells; thereby
interfering with regeneration of reduced glutathione needed
to prevent oxidative denaturation of haemoglobin (Thrall,
2004). Denaturated haemoglobin, when developed, precipitates
on the surface of red blood cells (named Heinz bodies)
and triggers intra- and extravascular haemolysis (Lincoln et
al., 1992; Tang et al., 2008).