Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma 73019.
Plant Physiol. 1990 Oct;94(2):745-51. doi: 10.1104/pp.94.2.745.
Three dicarbonyl reagents were used to demonstrate the presence of an essential arginine residue in the NO(3) (-) uptake system from corn seedling roots (Zea mays L., Golden Cross Bantam). Incubation of corn seedlings with 2,3-butanedione (0.125-1.0 millimolar) and 1,2-cyclohexanedione (0.5-4.0 millimolar) in the presence of borate or with phenylglyoxal (0.25-2.0 millimolar) at pH 7.0 and 30 degrees C resulted in a time-dependent loss of NO(3) (-) uptake following pseudo-first-order kinetics. Second-order rate constants obtained from slopes of linear plots of pseudo-first-order rate constants versus reagent concentrations were 1.67 x 10(-2), 0.68 x 10(-2), and 1.00 x 10(-2) millimolar per minute for 2,3-butanedione, 1,2-cyclohexanedione, and phenylglyoxal, respectively, indicating the faster rate of inactivation with 2,3-butanedione at equimolar concentration. Double log plots of pseudo-first-order rate constants versus reagent concentrations yielded slope values of 1.031 (2,3-butanedione), 1.004 (1,2-cyclohexanedione), and 1.067 (phenylglyoxal), respectively, suggesting the modification of a single arginine residue. The effectiveness of the dicarbonyl reagents appeared to increase with increasing medium pH from 5.5 to 8.0. Unaltered K(m) and decreased V(max) in the presence of reagents indicate the inactivation of the modified carriers with unaltered properties. The results thus obtained indicate that the NO(3) (-) transport system possesses at least one essential arginine residue.
三种二羰基试剂被用于证明玉米幼苗根部（Zea mays L.，Golden Cross Bantam）中硝酸盐（NO3-）摄取系统存在必需的精氨酸残基。在硼酸或苯乙醛存在下，用 2,3-丁二酮（0.125-1.0 毫摩尔）和 1,2-环己二酮（0.5-4.0 毫摩尔）在 pH 值 7.0 和 30°C 下孵育玉米幼苗，导致 NO3-摄取按照拟一级动力学呈现时间依赖性损失。从拟一级速率常数与试剂浓度的线性图斜率获得的二级速率常数分别为 2,3-丁二酮、1,2-环己二酮和苯乙醛的 1.67×10-2、0.68×10-2 和 1.00×10-2 毫摩尔/分钟，表明在等摩尔浓度下，2,3-丁二酮的失活速度更快。拟一级速率常数与试剂浓度的双对数图产生的斜率值分别为 2,3-丁二酮的 1.031、1,2-环己二酮的 1.004 和苯乙醛的 1.067，表明单个精氨酸残基被修饰。二羰基试剂的有效性似乎随着介质 pH 值从 5.5 增加到 8.0 而增加。在试剂存在下，Km 不变且 Vmax 降低，表明修饰载体失活但特性不变。因此，结果表明硝酸盐（NO3-）转运系统至少存在一个必需的精氨酸残基。
