Hanson K R, Peterson R B
Arch Biochem Biophys. 1987 Feb 1;252(2):591-605. doi: 10.1016/0003-9861(87)90066-x.
We showed previously [K.R. Hanson and R.B. Peterson (1986) Arch. Biochem. Biophys. 246, 332-346] that under steady-state photosynthetic conditions the fraction of ribulose bisphosphate oxidized and the fraction of glycolate carbon photorespired (the stoichiometry of photorespiration) may be estimated in leaves by a combination of physical and stereochemical methods. The calculations assumed that when (3R)-D-[3-3H1,3-14C]glyceric acid is supplied to illuminated leaf discs the only loss of 3H from the combined photosynthetic and photorespiratory system is the result of glycolate oxidase action; i.e., the isomerase-catalyzed losses in the regeneration of ribulose bisphosphate are negligible. The present study of tobacco leaf discs under zero-photorespiration conditions (low O2 and high CO2 concentrations), and also of maize leaf discs, shows that some 3H losses occur (between 8 and 13% of the 3H at C-1 of ribulose 5-phosphate). The calculated loss varied moderately with temperature but did not vary when the flux of ribulose bisphosphate formation was altered by changing the irradiance. The calculated loss under zero-photorespiration conditions, therefore, may be used to calculate ribulose bisphosphate and glycolate partitioning under other conditions. Earlier experiments on the influence of O2 and CO2 concentrations of temperature on the partitioning of ribulose bisphosphate and glycolate have been reexamined. The loss corrections decreased all values for the fraction of ribulose bisphosphate oxidized and increased all values for the stoichiometry of photorespiration. Essentially all stoichiometry values were above the theoretical lower limit of 25%. The previous conclusion that the stoichiometry of photorespiration substantially exceeds 25% at higher O2 concentrations and higher temperatures is unchanged. The results with maize leaf discs implied that there is very little oxidation of ribulose 1,5-bisphosphate under normal-air conditions; i.e., photorespiration is indeed suppressed, not merely hidden, by efficient refixation of CO2.
我们之前已经表明[K.R. 汉森和R.B. 彼得森（1986年）《生物化学与生物物理学文献》246卷，332 - 346页]，在稳态光合条件下，可通过物理和立体化学方法相结合来估算叶片中被氧化的二磷酸核酮糖的比例以及光呼吸的乙醇酸碳的比例（光呼吸的化学计量）。这些计算假设，当向光照下的叶圆片供应(3R)-D-[3-³H,¹³C]甘油酸时，光合和光呼吸系统中³H的唯一损失是乙醇酸氧化酶作用的结果；即，二磷酸核酮糖再生过程中异构酶催化的损失可忽略不计。目前对零光呼吸条件下（低氧和高二氧化碳浓度）的烟草叶圆片以及玉米叶圆片的研究表明，会发生一些³H损失（占5-磷酸核酮糖C-1位³H的8%至13%）。计算得出的损失随温度有一定程度的变化，但当通过改变光照强度改变二磷酸核酮糖形成通量时，损失并未改变。因此，零光呼吸条件下计算得出的损失可用于计算其他条件下二磷酸核酮糖和乙醇酸的分配情况。对之前关于氧气和二氧化碳浓度以及温度对二磷酸核酮糖和乙醇酸分配影响的实验进行了重新审视。损失校正降低了所有被氧化的二磷酸核酮糖比例的值，并提高了所有光呼吸化学计量的值。基本上所有化学计量值都高于理论下限25%。之前关于在较高氧气浓度和较高温度下光呼吸化学计量大幅超过25%的结论并未改变。玉米叶圆片的结果表明，在正常空气条件下1,5-二磷酸核酮糖的氧化很少；即，通过有效的二氧化碳再固定，光呼吸确实受到抑制，而不仅仅是被掩盖。
