Arnason T, Sinclair J
Biochim Biophys Acta. 1976 Jun 8;430(3):517-23. doi: 10.1016/0005-2728(76)90027-x.
The modulated oxygen polarography has been used to study the rate-determining steps of photosynthetic oxygen evolution in spinach chloroplasts. The rate constant, k, of the reaction has a value of 218 +/- 10 (S.E.) s-1 at 23 degrees C and an activation energy of 7 +/- 2 (S.E.) kcal-mol-1. A kinetic isotope experiment indicated that this step is probably not the water-splitting reaction. These findings resemble previous results with the unicellular alga Chlorella (Sinclair, J. and Arnason, T (1974) Biochim. Biophys. Acta 368, 393-400). In other experiments we changed the pH, O2 concentration and osmolarity of the medium, and treated the chloroplasts with 1 mM NH4Cl without detecting any significant change in k. These results suggest that the step is irreversible. However, a significantly lower value of k, 110 +/- 20 (S.E.) s-1 was obtained when all salts except 1 mM MgCl2 were removed from the medium bathing the chloroplasts.
调制氧极谱法已被用于研究菠菜叶绿体中光合放氧的速率决定步骤。该反应的速率常数k在23℃时为218±10（标准误差）s⁻¹，活化能为7±2（标准误差）kcal·mol⁻¹。一项动力学同位素实验表明，该步骤可能不是水裂解反应。这些发现与之前对单细胞藻类小球藻的研究结果相似（辛克莱尔，J.和阿纳森，T（1974年）《生物化学与生物物理学报》368，393 - 400）。在其他实验中，我们改变了培养基的pH值、氧气浓度和渗透压，并用1 mM氯化铵处理叶绿体，但未检测到k有任何显著变化。这些结果表明该步骤是不可逆的。然而，当从叶绿体悬浮培养基中去除除1 mM氯化镁以外的所有盐时，得到了显著更低的k值，即110±20（标准误差）s⁻¹。
