Heavy metal binding properties of earthworm chloragosomes

The highest concentration of metal in Lumbricus terrestris and Lumbricus rubellus chloragosomes was Ca++ folowed by Fe+++, Zn++ and Mg++. Chloragosomes and body wall extracts bound Pb++ and to a lesser extent Cu++ but not Zn++. Binding of Pb++ and Cu++ was greater in chloragosomes than body wall homogenate. Maximum binding capacity for Pb++ was higher in Lumbricus terrestris than Lumbricus rubellus. The binding of Pb++ to chloragosomes appears to be unrelated to phospholipid content. The release of most Zn++ and Ca++ in chloragosomes by 0.01 M HCl but release of Fe+++ requiring 5 M HCl suggests that the latter may be in the form of an organometallic complex. Release of Cu++ from chloragosomes by 0.001 M HCl but only 20% of the bound Pb++ indicates that Pb++ is more firmly bound to chloragosomes than Cu++. Bound Pb++ in body wall extracts is released by 0.001 M HCl. The addition of Pb++ to a chloragosomal suspension caused a drop in pH and release of mainly Ca++ with smaller amounts of Zn++ and Mg++ indicating a cation exchange was taking place. It is concluded that earthworm chloragosomes bind heavy metal by a cation-exchange system which may be related to the chemical constituents of chloragosomes being similar to ion exchange compounds.