Demonstration of high-affinity Mn²⁺ uptake in Saccharomyces cerevisiae: Specificity and kinetics

TY - JOUR

T1 - Demonstration of high-affinity Mn2+ uptake in Saccharomyces cerevisiae

T2 - Specificity and kinetics

AU - Gadd, Geoffrey M.

AU - Laurence, Oliver S.

PY - 1996/5/1

Y1 - 1996/5/1

N2 - The existence of multiple transport systems for Mn2+ in Saccharomyces cerevisiae has been demonstrated in this study. Mn2+ (supplied as MnCl2) was accumulated by S. cerevisiae at all Mn2+ concentrations examined (25 nM-1 mM) but a log-log plot of uptake rates and total amounts accumulated revealed the existence of at least two Mn2+-concentration-dependent transport systems. Over a low Mn2+ concentration range (25-1000 nM), high-affinity Mn2+ uptake occurred with a Km value of 0.3 μM, while transformation of kinetic data obtained over the concentration range 5-200 μM revealed another system with a Km of 62 μM. Meaningful kinetic analyses were not possible at higher Mn2+ concentrations because of toxicity: only about 30% of cells remained viable after 30 min incubation with 1000 μM MnCl2. Release of K+ accompanied Mn2+ accumulation and this increased with increasing Mn2+ concentration. However, even in non-toxic Mn2+ concentrations, the ratio of Mn2+ uptake to K+ release greatly exceeded electroneutral stoichiometric exchange. In 50 μM MnCl2, the ratio was 1:123 and this increased to 1:2670 in 1000 μM MnCl2, a toxic concentration. External Mg2+ was found to decrease Mn2+ accumulation at all concentrations examined, but to differing extents. Over the low Mn2+ concentration range (5-200 μM), Mg2+ competitively inhibited Mn2+ uptake with a half-maximal inhibitory concentration, Ki, of 5.5 μM Mg2+. However, even in the presence of a 50-fold excess of Mg2+, inhibition of Mn2+ uptake was of the order of 72% and it appears that the cellular requirement for Mn2+ could be maintained even in the presence of such a large excess of Mg2+. Over the high Mn2+ concentration range (5-200 μM), the Ki for Mg2+ was 25.2 μM. At low Mn2+ concentrations, Zn2+ and Co2+, but not Cd2+, inhibited Mn2+ uptake, which indicated that the high-affinity Mn2+ uptake system was of low specificity, while at higher Mn2+ concentrations, where the lower-affinity Mn2+ transport system operated, inhibition was less marked. However, competition studies with potentially toxic metal cations were complicated due to toxic effects, particularly noticeable at 50 μM Co2+ and Cd2+.

AB - The existence of multiple transport systems for Mn2+ in Saccharomyces cerevisiae has been demonstrated in this study. Mn2+ (supplied as MnCl2) was accumulated by S. cerevisiae at all Mn2+ concentrations examined (25 nM-1 mM) but a log-log plot of uptake rates and total amounts accumulated revealed the existence of at least two Mn2+-concentration-dependent transport systems. Over a low Mn2+ concentration range (25-1000 nM), high-affinity Mn2+ uptake occurred with a Km value of 0.3 μM, while transformation of kinetic data obtained over the concentration range 5-200 μM revealed another system with a Km of 62 μM. Meaningful kinetic analyses were not possible at higher Mn2+ concentrations because of toxicity: only about 30% of cells remained viable after 30 min incubation with 1000 μM MnCl2. Release of K+ accompanied Mn2+ accumulation and this increased with increasing Mn2+ concentration. However, even in non-toxic Mn2+ concentrations, the ratio of Mn2+ uptake to K+ release greatly exceeded electroneutral stoichiometric exchange. In 50 μM MnCl2, the ratio was 1:123 and this increased to 1:2670 in 1000 μM MnCl2, a toxic concentration. External Mg2+ was found to decrease Mn2+ accumulation at all concentrations examined, but to differing extents. Over the low Mn2+ concentration range (5-200 μM), Mg2+ competitively inhibited Mn2+ uptake with a half-maximal inhibitory concentration, Ki, of 5.5 μM Mg2+. However, even in the presence of a 50-fold excess of Mg2+, inhibition of Mn2+ uptake was of the order of 72% and it appears that the cellular requirement for Mn2+ could be maintained even in the presence of such a large excess of Mg2+. Over the high Mn2+ concentration range (5-200 μM), the Ki for Mg2+ was 25.2 μM. At low Mn2+ concentrations, Zn2+ and Co2+, but not Cd2+, inhibited Mn2+ uptake, which indicated that the high-affinity Mn2+ uptake system was of low specificity, while at higher Mn2+ concentrations, where the lower-affinity Mn2+ transport system operated, inhibition was less marked. However, competition studies with potentially toxic metal cations were complicated due to toxic effects, particularly noticeable at 50 μM Co2+ and Cd2+.

KW - Divalent cations

KW - Mg

KW - Mn

KW - Saccharomyces cerevisiae

KW - Transport kinetics

UR - https://www.scopus.com/pages/publications/0029920224

U2 - 10.1099/13500872-142-5-1159

DO - 10.1099/13500872-142-5-1159

M3 - Article

C2 - 8704957

AN - SCOPUS:0029920224

SN - 1350-0872

VL - 142

SP - 1159

EP - 1167

JO - Microbiology

JF - Microbiology

IS - 5

ER -