Department of Life Sciences and Dry-Lands Research Institute, University of California, Riverside, California 92502.
Plant Physiol. 1967 May;42(5):712-8. doi: 10.1104/pp.42.5.712.
The kinetics of (14)CO(2) carboxylation and decarboxylation in corn root tips were determined to ascertain the sequence of product formation and subsequent utilization, and to obtain further evidence to predict the enzymes mediating the carboxylation and decarboxylations. The carboxylation data indicated that the first product was oxaloacetate followed by malate and aspartate. Malate was the first stable product which could be detected. Decarboxylation data indicated that a large fraction of the (14)CO(2) release and turnover of (14)C was accountable for by a decrease in malate: however, essentially all labeled amino acids turned over rapidly and at a greater rate than organic acids. The data generally support the hypothesis that CO(2) fixation in corn root tips is via P-enolpyruvate carboxylase and malic dehydrogenase and that subsequent malate metabolism is for the most part by direct decarboxylation, possibly by the malic enzyme.
测定了玉米根尖（14）CO2的羧化和脱羧动力学，以确定产物形成的顺序和随后的利用，并获得进一步的证据来预测介导羧化和脱羧的酶。羧化数据表明，第一个产物是草酰乙酸，然后是苹果酸和天冬氨酸。苹果酸是第一个可以检测到的稳定产物。脱羧数据表明，（14）CO2释放和（14）C周转的大部分可归因于苹果酸的减少：然而，基本上所有标记的氨基酸都迅速且以比有机酸更快的速率周转。这些数据普遍支持这样的假设，即玉米根尖的 CO2 固定是通过 P-烯醇丙酮酸羧化酶和苹果酸脱氢酶进行的，随后的苹果酸代谢主要通过直接脱羧进行，可能通过苹果酸酶进行。
