Chen C, Gibbs M
Institute for Photobiology of Cells and Organelles, Brandeis University, Waltham, Massachusetts 02254.
Plant Physiol. 1991 Jan;95(1):82-7. doi: 10.1104/pp.95.1.82.
Chloroplastic respiration was monitored by measuring (14)CO(2) from (14)C glucose in the darkened Chlamydomonas reinhardtii F-60 chloroplast. The patterns of (14)CO(2) evolution from labeled glucose in the absence and presence of the inhibitors iodoacetamide, glycolate-2-phosphate, and phosphoenolpyruvate were those expected from the oxidative pentose phosphate cycle and glycolysis. The K(m) for glucose was 56 micromolar and for MgATP was 200 micromolar. Release of (14)CO(2) was inhibited by phloretin and inorganic phosphate. Comparing the inhibition of CO(2) evolution generated by pH 7.5 with respect to pH 8.2 (optimum) in chloroplasts given C-1, C-2, and C-6 labeled glucose indicated that a suboptimum pH affects the recycling of the pentose phosphate intermediates to a greater extent than CO(2) evolution from C-1 of glucose. Respiratory inhibition by pH 7.5 in the darkened chloroplast was alleviated by NH(4)Cl and KCl (stromal alkalating agents), iodoacetamide (an inhibitor of glyceraldehyde 3-phosphate dehydrogenase), or phosphoenolpyruvate (an inhibitor of phosphofructokinase). It is concluded that the site which primarily mediates respiration in the darkened Chlamydomonas chloroplast is the fructose-1,6-bisphosphatase/phosphofructokinase junction. The respiratory pathways described here can account for the total oxidation of a hexose to CO(2) and for interactions between carbohydrate metabolism and the oxyhydrogen reaction in algal cells adapted to a hydrogen metabolism.
通过测量黑暗条件下莱茵衣藻F-60叶绿体中来自¹⁴C葡萄糖的¹⁴CO₂来监测叶绿体呼吸。在不存在和存在抑制剂碘乙酰胺、磷酸乙醇酸和磷酸烯醇丙酮酸的情况下，标记葡萄糖释放¹⁴CO₂的模式符合氧化戊糖磷酸途径和糖酵解的预期。葡萄糖的米氏常数（Kₘ）为56微摩尔，MgATP的米氏常数为200微摩尔。根皮素和无机磷酸盐可抑制¹⁴CO₂的释放。比较给予C-1、C-2和C-6标记葡萄糖的叶绿体中pH 7.5相对于pH 8.2（最适pH）对CO₂释放的抑制作用，结果表明，次适pH对戊糖磷酸中间产物循环的影响比对葡萄糖C-1位CO₂释放的影响更大。黑暗叶绿体中pH 7.5引起的呼吸抑制可通过NH₄Cl和KCl（基质碱化剂）、碘乙酰胺（甘油醛3-磷酸脱氢酶抑制剂）或磷酸烯醇丙酮酸（磷酸果糖激酶抑制剂）得到缓解。得出的结论是，黑暗条件下衣藻叶绿体中主要介导呼吸作用的位点是果糖-1,6-二磷酸酶/磷酸果糖激酶连接点。这里描述的呼吸途径可以解释己糖完全氧化为CO₂的过程，以及适应氢代谢的藻类细胞中碳水化合物代谢与氢氧反应之间的相互作用。
