Scanning Microscopy


This paper surveys the literature on the use of EPXMA in conjunction with (heavy metal) pollution studies.

Metal-accumulating compartments are usually granules or vacuoles of 6 main types (i) extracellular, soluble and fairly pure calcium carbonate granules; (ii) insoluble, calcium and phosphorus-rich granules, of ten containing several metal contaminants; (iii) multifunctional, calcium and phosphorus granules containing a high proportion of rather complex organic molecules; (iv) copper-(and sulphur) rich granules; (v) iron-(and phosphorus) rich granules; (vi) Cd, Zn, Cu and Hg -containing vacuoles, where the metals are presumably complexed with cysteine-rich metallothionein proteins, or their derivatives. With a few exceptions, types (ii)-(vi) are intracellular. Many of these inclusions may be associated with the lysosomal system, and the metals are sequestered by the various compartments due to their ligand-binding properties (i.e., whether they belong to Class A or Class B) and on the availability of pre-existing or inducible ligands within those compartments. Future biochemical analysis may change the categories presented here; for example, some type (iv) granules may well be found to contain metallothionein, and thus they may be more appropriately described as type (vi) inclusions.

It is concluded that EPXMA provides unique multi-element information concerning the metabolism of essential and toxic heavy metals within cells. However, this information may be considerably enhanced by the use of complementary experimental methods.

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