Deane E M, O'Brien R W
Arch Microbiol. 1975 Nov 7;105(3):295-301. doi: 10.1007/BF00447149.
The intracellular concentration of inorganic 35SO4 in Monochrysis lutheri cells exposed to 0.513 mM Na235SO4 for up to 6-hr remained constant at about 0.038 mM. The exchange rate of this 35SO4 with the external unlabelled sulphate was negligible compared to the rate of influx across the plasmalemma (0.032 mu moles/g cells/hr). The flux of free 35SO4 to organic 35S was 0.029 mu moles/g cells/hr. Assuming an internal electrical potential in the cells of -70 mV, this intracellular concentration of inorganic 35SO4 was well in excess of that obtainable by passive diffusion as calculated from the Nernst equation. These results indicate that sulphate is accumulated by an active mechanism rather than by facilitated diffusion. Sulphate uptake appears to occur via a carrier-mediated membrane transport system which conforms to Michaelis-Menten type saturation kinetics with a Km of 3.2 X 10(-5) M and Vmax of 7.9 X 10(-5) mu moles sulphate/hr/10(5) cells. Uptake was dependent on a source of energy since the metabolic inhibitor CCCP almost completely inhibited uptake under both light and dark conditions and DCMU caused a 50% decrease in uptake under light conditions. Under dark conditions, uptake remained at about 80% of that observed under light conditions and was little affected by DCMU, indicating that the energy for uptake could be supplied by either photosynthesis or respiration. A charge and size recognition site in the cell is implied by the finding that sulphate uptake was inhibited by chromate and selenate but not by tungstate, molybdate, nitrate or phosphate. Chromate did not inhibit photosynthesis. Cysteine and methionine added to the culture medium were apparently capable of exerting inhibition of sulphate uptake in both unstarved and sulphate-starved cells. Cycloheximide slightly inhibited sulphate uptake over an 8-hr period indicating, either a slow rate of entry of the inhibitor into the cells or a slow turnover of the protein(s) associated with sulphate transport.
将等鞭金藻细胞暴露于0.513 mM的Na₂³⁵SO₄中长达6小时，其细胞内无机³⁵SO₄的浓度保持恒定，约为0.038 mM。与³⁵SO₄跨质膜流入的速率（0.032微摩尔/克细胞/小时）相比，这种³⁵SO₄与外部未标记硫酸盐的交换速率可忽略不计。游离³⁵SO₄向有机³⁵S的通量为0.029微摩尔/克细胞/小时。假设细胞内的电势为 -70 mV，根据能斯特方程计算，这种细胞内无机³⁵SO₄的浓度远超过通过被动扩散所能达到的浓度。这些结果表明，硫酸盐是通过主动机制而非易化扩散积累的。硫酸盐的摄取似乎是通过一种载体介导的膜转运系统进行的，该系统符合米氏类型的饱和动力学，Km为3.2×10⁻⁵ M，Vmax为7.9×10⁻⁵微摩尔硫酸盐/小时/10⁵个细胞。摄取依赖于能量来源，因为代谢抑制剂羰基氰化物间氯苯腙（CCCP）在光照和黑暗条件下几乎完全抑制摄取，而敌草隆（DCMU）在光照条件下使摄取减少50%。在黑暗条件下，摄取量约为光照条件下的80%，且受DCMU的影响较小，这表明摄取所需的能量可以由光合作用或呼吸作用提供。铬酸盐和硒酸盐抑制硫酸盐摄取，而钨酸盐、钼酸盐、硝酸盐或磷酸盐则不抑制，这一发现暗示细胞中存在电荷和大小识别位点。铬酸盐不抑制光合作用。添加到培养基中的半胱氨酸和蛋氨酸显然能够抑制未饥饿和硫酸盐饥饿细胞中的硫酸盐摄取。放线菌酮在8小时内略微抑制硫酸盐摄取，这表明要么抑制剂进入细胞的速率较慢，要么与硫酸盐转运相关的蛋白质周转较慢。
