The uptake of hydrogen sulfide (H(2)S) by shoots of curly kale (Brassica oleracea) showed saturation kinetics with respect to the atmospheric concentration. The kinetics are largely determined by the rate of metabolism of the absorbed H(2)S into cysteine, catalyzed by O-acetylserine (thiol)lyase, and can be described by the Michaelis-Menten equation. When B. oleracea was grown under sulfate (SO(4)(2-))-deprived conditions, plants developed sulfur (S) deficiency symptoms and H(2)S uptake kinetics were substantially altered. Shoots of SO(4)(2-)-deprived plants had a lower affinity to H(2)S uptake, whereas the maximal H(2)S uptake rate was higher. When SO(4)(2-)-deprived plants were simultaneously exposed to 0.2 &mgr;l l(-1) H(2)S all S deficiency symptoms disappeared and H(2)S uptake kinetics returned rapidly to values observed for S-sufficient shoots. The activity of the H(2)S-fixating enzyme O-acetylserine (thiol)lyase was hardly affected upon either prolonged H(2)S exposure or SO(4)(2-) deprivation. Evidently, the activity of O-acetylserine (thiol)lyase was not the rate-limiting step in the H(2)S uptake by shoots. The significance of the in situ availability and rate of synthesis of the substrate O-acetylserine for O-acetylserine (thiol)lyase as determining factor in the uptake kinetics of H(2)S needs further evaluation.

中文翻译：

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大气硫化氢作为甘蓝的硫源：硫化氢吸收动力学和 O-乙酰丝氨酸（硫醇）裂解酶活性受硫营养影响

卷曲羽衣甘蓝 (Brassica oleracea) 枝条对硫化氢 (H(2)S) 的吸收显示出相对于大气浓度的饱和动力学。动力学主要由吸收的 H(2)S 代谢为半胱氨酸的速率决定，由 O-乙酰丝氨酸（硫醇）裂解酶催化，并且可以由 Michaelis-Menten 方程描述。当 B.oleracea 生长在硫酸盐 (SO(4)(2-))-剥夺条件下时，植物开发硫 (S) 缺乏症状和 H(2)S 吸收动力学被大大改变。SO(4)(2-)-剥夺植物的芽对H(2)S 吸收具有较低的亲和力，而最大H(2)S 吸收率较高。当没有 SO(4)(2-) 的植物同时暴露于 0.2 &mgr; ll(-1) H(2)S 所有 S 缺乏症状都消失了，并且 H(2)S 吸收动力学迅速恢复到 S 充足芽观察到的值。H(2)S-固定酶O-乙酰丝氨酸(硫醇) 裂解酶的活性几乎不受长时间H(2)S 暴露或SO(4)(2-) 剥夺的影响。显然，O-乙酰丝氨酸（硫醇）裂解酶的活性不是 H(2)S 被枝条吸收的限速步骤。O-乙酰丝氨酸（硫醇）裂解酶的原位可用性和底物 O-乙酰丝氨酸的合成速率作为 H(2)S 吸收动力学的决定因素的重要性需要进一步评估。O-乙酰丝氨酸（硫醇）裂解酶的活性不是枝条吸收 H(2)S 的限速步骤。O-乙酰丝氨酸（硫醇）裂解酶的原位可用性和底物 O-乙酰丝氨酸的合成速率作为 H(2)S 吸收动力学的决定因素的重要性需要进一步评估。O-乙酰丝氨酸（硫醇）裂解酶的活性不是枝条吸收 H(2)S 的限速步骤。O-乙酰丝氨酸（硫醇）裂解酶的原位可用性和底物 O-乙酰丝氨酸的合成速率作为 H(2)S 吸收动力学的决定因素的重要性需要进一步评估。