The mechanism of metal binding to glutaraldehyde-fixed noradrenaline-storing adrenomedullary granules.

Abstract

The binding mechanism of a wide spectrum of metals to glutaraldehydefixed, noradrenaline-storing granules has been studied with histochemical methods. It has been established that both metal binding and reducing properties of these granules cepend on the presence of phenolic hydroxyl groups. The assumption, based onin vitro experiments, that free aldehyde groups derived from glutaraldehyde account for the reducing properties of noradrenaline granules is proved to be unacceptable. It is pointed out that the two types of metal binding reactions to glutaraldehyde-fixed noradrenaline granules are probably related to the tendency of theo-dihydroxy grouping, both for reduction and complex formation. An oxidation-reduction mechanism has been demonstrated in the binding of permanganate and that of low pH hexavalent chromium. The preservation of the reducing properties of the metal binding substance after the binding of osmium tetroxide, high pH hexavalent chromium, hexavalent molybdenum, cupric and ferrous ions is explained by complex formation. In the case of osmium tetroxide, this concept is further supported by the finding that the valence-state of osmium is not lowered after binding to glutaraldehyde-fixed noradrenaline granules. The previously described histochemical reaction for the demonstration of the dual affinity of hexavalent chromium for glutaraldehyde-fixed noradrenaline granules is proved to depend on the oxidation state of the bound chromium.