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Summary: Uptake of 54Mn from 10 nM-Mn2+ was shown to be both energy-and pH-dependent. Analysis of the uptake kinetics revealed an apparent half-saturation constant, K t of 16·4 nM-Mn2+ and a maximal rate of transport, V max,of l·01 nmol Mn2+ (g dry wt)−1 min−1 Mn2+ uptake was highly specific, being unaffected by 100-fold molar excess of Mg2+, zn2+, Ca2+, Co2+, Ni2+ and Cu2+; however, uptake was inhibited 30 to 40% by 1000-fold molar excess of Mg2+, Zn2+, Ca2+, Co2+ and Ni2+. Zn2+ competitively inhibited Mn2+ uptake, theK i value being approximately 500-fold greater than the Kt for Mn2+. Efflux studies indicated that metabolic exchange of 54Mn occurred to a small extent. Cellular Mn2+ contents remained relatively constant during growth in batch culture. The Mn2+ transport system observed appears to be analogous to the specific metal transport systems reported in bacteria.
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