Wu G
Biochemistry Section, National Institute for Minamata Disease, Kumamoto, Japan.
J Appl Toxicol. 1998 Jan-Feb;18(1):55-61. doi: 10.1002/(sici)1099-1263(199801/02)18:1<55::aid-jat478>3.0.co;2-l.
Previous studies have investigated a number of possible transport systems for the uptake of methylmercury (MeHg) in erythrocytes. In the present study, three additional systems were studied. The uptake of MeHg by isolated erythrocytes from rats was studied at 5 degrees C and 20 degrees C. Glutamine was used to test system N and system y+, and glycylglycine was used to test the oligopeptide-H+ transport system. The Hill equation was used in kinetic analysis. The results show that both glutamine and glycylglycine stimulated the uptake of MeHg, but the stimulation by glycylglycine is stronger than by glutamine, and the stimulation at 5 degrees C is stronger than at 20 degrees C (mean values are 167.98% and 83.68% in the glycylglycine group at 5 degrees C and 20 degrees C versus 26.28% and 19.23% in the glutamine group at 5 degrees C and 20 degrees C). The kinetic analysis shows that: the Michaelis-Menten constant Km increased as temperature increased in both groups and was larger in experimental groups than in control groups; the Hill constants increased as temperature increased in both groups and were smaller in experimental groups than in control groups; and as temperature increased, maximum velocity Vmax increased in control groups and decreased in experimental groups, and was larger in experimental groups than in control groups, with the exception of the glycylglycine group at 20 degrees C. The results demonstrated that system N, system y+ and oligopeptide-H+ transport systems were not involved in the in vitro uptake of MeHg into erythrocytes. The stimulation by glutamine and glycylglycine might be related to some signalling pathways, through which nitric oxide and oligopeptide serve as messengers and cause functional alterations in the uptake of MeHg.
以往的研究已经探究了红细胞摄取甲基汞（MeHg）的多种可能的转运系统。在本研究中，又对另外三种系统进行了研究。在5℃和20℃下研究了大鼠分离红细胞对MeHg的摄取。使用谷氨酰胺来测试系统N和系统y+，并使用甘氨酰甘氨酸来测试寡肽-H+转运系统。在动力学分析中使用了希尔方程。结果表明，谷氨酰胺和甘氨酰甘氨酸均刺激了MeHg的摄取，但甘氨酰甘氨酸的刺激作用强于谷氨酰胺，且5℃时的刺激作用强于20℃时（甘氨酰甘氨酸组在5℃和20℃时的平均值分别为167.98%和83.68%，而谷氨酰胺组在5℃和20℃时分别为26.28%和19.23%）。动力学分析表明：两组的米氏常数Km均随温度升高而增加，且实验组中的Km大于对照组；两组的希尔常数均随温度升高而增加，且实验组中的希尔常数小于对照组；随着温度升高，对照组的最大速度Vmax增加，而实验组的Vmax降低，且实验组中的Vmax大于对照组，但20℃时的甘氨酰甘氨酸组除外。结果表明，系统N、系统y+和寡肽-H+转运系统均不参与体外MeHg进入红细胞的摄取过程。谷氨酰胺和甘氨酰甘氨酸的刺激作用可能与某些信号通路有关，通过这些信号通路，一氧化氮和寡肽作为信使，导致MeHg摄取功能发生改变。
