摘要
豌豆幼苗叶片线粒体中,Gly,Mal和Isocit的氧化速率均受光促进。Gly的氧化抑制Mal和Isocit的氧化,而其本身不受影响。用INH抑制Gly氧化或提高NAD^+浓度均会降低其抑制程度。线粒体氧化Gly,Mal和Isocit的K_m(NAD^+)分别为66.67,119.1μmol/L和152.2μmol/L。Gly抑制Mal和Isocit氧化是由于Gly氧化在竞争NAD^+中占优势。
The effect of glycine oxidation on malate and isocitrate oxidation in mitochondriaisolated from pea seedling leaves was investigated with oxygen electrode and isotopic tracer technique.
The oxidation rates of glycine, malate and isocitrate were stimulated by illumination. Malate or isocitrate oxidation was inhibited by concurrent oxidation of glycine, but glycine oxidation was not affected by concurrent oxidation of malate or isocitrate. Increasing glycine concentration increased, and the addition of INH, the inhibitor of glycine decarboxylase, decreased the percentage of inhibition of malate or isocitrate oxidation by glycine oxidation.
The degree of inhibition of malate or isocitrate oxidation by concurrent oxidation of glycine decreased with increasing NAD^+ concentration. The K_m values of glycine, malate and isocitrate oxidation by isolated mitochondria for NAD^+ were found to be 66.67, 119.05 μmol/L and 152.20 μmol/L, respectively. This means that the ability of glycine oxidation to compete for available NAD^+ within mitochondria is stronger than that of the oxidation of the other substrates. This behaviour was more pronounced at lower concentrations of NAD^+ This is the reason why malate or isocitrate oxidation was inhibited by concurrent oxidation of glycine, but not the other way round.
According to these results, we conclude that the TCA cycle in the mitochondria continues to operate in light. But in photosynthetic tissues, the turnover of TCA cycle is partially inhibited in light. This is because glycine oxidation competes favorably with NAD^+ dependent oxidation of TCA cycle acids for NAD^+ within the mitochondria, resulting in partial inhibition of the activity of the TCA cycle. The turnover of TCA cycle in photosynthetic tissues is thus limited by photorespiratory oxidative decarboxylation of glycine in the light, which is a self-control mechanism formed by the plants during their long period of evolution.
基金
The Project is Supported by National Natural Science Foundation of China
关键词
豌豆
线粒体
甘氨酸
苹果酸
氧化
glycine oxidation, malate oxidation, isocitrate oxidation, pea, mitochondria
