Missing information in bio-inorganic chemistry

The forms of Ni in soil are diverse and range from those of high activity (water-soluble and exchangeable forms) to ones that have no reactivity in the short term (the life of a plant). The reactions of Ni are dominated by sorption reactions on soil colloids whose nature, relative proportions, and concentrations are important. Soil pH plays a major role in these reactions and thus influences the availability of Ni to plants quite markedly; few other factors appear to be as significant as pH. Deficiency of Ni in plants is unlikely to be a practical problem, but toxicity is more likely. Interest in the occurrence of Ni toxicity is dominated by research on serpentine soils (ancient Ni) and soils to which large quantities of Ni have been added in wastes (modern Ni), particularly in the forms of sewage and sewage sludge. Much of the understanding of the forms and reactions of Ni in soils comes from experiments dealing with the chemistry and biology of these two extreme situations. Needless to say, caution is essential when attempting to determine what is normal. Future research on Ni in soil could fruitfully pursue, for example, the role of microbes in influencing the behavior of Ni, the fractionation of Ni in studies of weathering and reversion of active forms of Ni to less active ones, and the speciation of Ni in the soil solution and the extent and cause of temporal changes.

The role of copper metallothionein (CuMT) in copper metabolism and metalloenzyme activation is poorly understood. We have chosen marine crustaceans, in which a direct correlation exists between levels of Cu(I)MT and Cu(I)-hemocyanin during the molt cycle (Engel and Brouwer, Biol. Bull. 173, 239-251, 1987) as unique model systems to study the involvement of MTs in metalloprotein activation and degradation. We have isolated three low-molecular weight, cysteine-rich copper proteins from the American lobster Homarus americanus, which we designate as CuMT-1, CuMT-2, and CuMT-3, respectively. As a first attempt to fully characterize these proteins, we have determined the sequence of the first 56 amino acids of CuMT-1. The results show this protein to belong to the class I MTs, i.e., related in primary structure to equine renal MT. CuMT-1 cannot transfer its copper to copper-depleted apohemocyanin. CuMT-2 belongs to the same class of MTs as CuMT-1, but CuMT-3 does not. The latter can reactivate lobster hemocyanin containing reduced amounts of Cu(I). Spectroscopic studies show that Cu(I) transfer from CuMT-3 to apohemocyanin initially results in the formation of distorted binuclear-copper sites, which subsequently slowly return to their native stereochemical configuration. Finally, we present evidence that shows that the class I MTs in marine Crustacea are involved in the sequestration of elevated levels of heavy-metal ions. These observations strongly suggest that the different forms of MT have different biological functions.