纤细裸藻在钴胺素充足和受限生长条件下的光合作用。
Photosynthesis of Euglena gracilis under Cobalamin-Sufficient and -Limited Growing Conditions.
作者信息
Isegawa Y, Nakano Y, Kitaoka S
机构信息
Department of Hygiene, Kobe University School of Medicine, Chuo-ku, Kobe 650, Japan.
出版信息
Plant Physiol. 1987 Jul;84(3):609-12. doi: 10.1104/pp.84.3.609.
Cobalamin is essential for growth of Euglena gracilis and photosynthesis. Methylcobalamin in Euglena chloroplasts (Y Isegawa, Y Nakano, S Kitaoka, 1984 Plant Physiol 76: 814-818) functions as a coenzyme of methionine synthetase. The requirement of cobalamin for photosynthesis appeared remarkably high in Euglena grown under the dark-precultured condition. The required amount of cobalamin for normal photosynthetic activity was 7.4 x 10(-11) molar, while 7.4 x 10(-10) molar cobalamin was required for normal growth. The lowered photosynthetic activity in cobalamin-limited cells was restored 20 hours after feeding cyanocobalamin or methionine to cobalamin-limited cells. Lowering of photosynthetic activity was due to loss of photosystem I activity. This photosynthetic activity was recovered after supplementation by methionine or cobalamin. The results suggest that methionine serves for the stabilization of photosystem I. This paper is the first report of the physiological function of cobalamin in chloroplasts of photosynthetic eukaryotes.
钴胺素对纤细裸藻的生长和光合作用至关重要。纤细裸藻叶绿体中的甲基钴胺素（Y Isegawa、Y Nakano、S Kitaoka，1984年《植物生理学》76: 814 - 818）作为甲硫氨酸合成酶的辅酶发挥作用。在黑暗预培养条件下生长的纤细裸藻中，钴胺素对光合作用的需求量显得非常高。正常光合作用活性所需的钴胺素量为7.4×10⁻¹¹摩尔，而正常生长需要7.4×10⁻¹⁰摩尔的钴胺素。在向钴胺素缺乏的细胞投喂氰钴胺素或甲硫氨酸20小时后，钴胺素缺乏细胞中降低的光合作用活性得以恢复。光合作用活性的降低是由于光系统I活性的丧失。补充甲硫氨酸或钴胺素后，这种光合作用活性得以恢复。结果表明甲硫氨酸有助于光系统I的稳定。本文是关于钴胺素在光合真核生物叶绿体中生理功能的首次报道。
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