METAL CHELATE REACTION OF ENTEROCHROMAFFIN

Enterochromaffin slowly binds ferrous ions at pH levels between 3.5 and 5.0 and gives them up again at low pH levels (1-2.5). Ferrous ions so bound may be demonstrated in situ by action of potassium ferricyanide, probably by acid dissociation of the chelate complex and precipitation of Turnbull's blue. This reaction is prevented by acetylation and tosylation, in agreement with the azo reaction. It is prevented by drastic oxidations but not by milder, sufficient to prevent azo coupling. This reaction was at first thought to indicate the presence of a substituent ortho to the phenolic hydroxyl of enterochromaffin, but in view of the occurrence of the reaction in model experiments with some para substituted phenols and phenylamines, after formaldehyde treatment, this conclusion must remain indefinite. Formaldehyde fixed serotonin model sections reacted relatively weakly, though giving strong reduction, azo and hematoxylin reactions.