Some Metabolic Effects of Rare-Earth Cations on Aspergillus Niger Cells

SUMMARY

When cells of Aspergillus niger are exposed to excess rare-earth cations, binding occurs rapidly and reaches a fixed maximum (1.25 × 10¹⁷ ions per mg dry-cell weight) within 30 min. Equal numbers of the different rare-earth cations are bound per unit mass of Aspergillus niger cells. Further, most of the rare-earth binding occurs on or in the cell surface with compounds other than lipids. Respiration and glucose utilization decrease with increasing quantities of cations bound until, at the maximal rare-earth binding capacity, glucose absorption is completely blocked. Cation concentrations which markedly depress or completely inhibit the oxidation of glucose do not change the endogenous rate of oxygen consumption. At molar concentrations ten times greater than that of the rare earth, disodium ethylenediamine tetraacetate (EDTA) and citric acid can, at a pH near their pKa values, completely reverse the blockage of glucose absorption and inhibition of oxidation produced by rare earths with cells of Aspergillus niger.