Knoth J, Isaacs J M, Njus D
J Biol Chem. 1981 Jul 10;256(13):6541-3.
Chromaffin granules have a translocator-mediated uptake system for the monoamines dopamine, serotonin, norepinephrine, and epinephrine. These substrates are predominantly cationic at physiological pH but they also exist in neutral, zwitterionic, and anionic forms. The cationic fraction is nearly pH-independent between pH 6.9 and pH 7.6. Over the same pH range, the neutral and zwitterionic fractions increase by a factor of 6.3 and the anionic fraction increases by a factor of 40. In chromaffin granule ghosts, the apparent Km values for dopamine and serotonin transport are independent of pH between 6.8 and 7.6. Consequently, the translocator probably binds the cationic form of the substrate. Vmax values for dopamine and serotonin uptake increase by a factor of 2 between pH 6.8 and pH 7.6.
嗜铬颗粒具有一种转运体介导的单胺类物质摄取系统，可摄取多巴胺、5-羟色胺、去甲肾上腺素和肾上腺素。这些底物在生理pH值下主要为阳离子形式，但它们也以中性、两性离子和阴离子形式存在。阳离子部分在pH 6.9至pH 7.6之间几乎与pH无关。在相同的pH范围内，中性和两性离子部分增加了6.3倍，阴离子部分增加了40倍。在嗜铬颗粒膜泡中，多巴胺和5-羟色胺转运的表观Km值在pH 6.8至7.6之间与pH无关。因此，转运体可能结合底物的阳离子形式。多巴胺和5-羟色胺摄取的Vmax值在pH 6.8至pH 7.6之间增加了2倍。
