叶绿体中醛缩酶的两种存在状态

小麦、水稻、大豆、烟草和菠菜叶绿体间质中的醛缩酶有两种存在状态,即可溶状态(S)和与层膜相结合的状态(M)。两种状态的醛缩酶的氨基酸组成上大体相同。两种状态可以相互转化,活性随植物的生育期而有明显的变化。醛缩酶在间质中的活性约为总活性的60％,与类囊体膜结合的约为40％。间质和层膜的醛缩酶的分子量分别为108KD和104KD。提纯菠菜叶绿体中与层膜结合的醛缩酶经盘状凝胶电泳,为一条均一的蛋白染色带。抗间质醛缩酶的免疫球蛋白对层膜醛缩酶有明显的沉淀反应。去污剂的强弱对“溶解”类囊体膜上的醛缩酶作用明显不同。

TWO FORMS OF ALDOLASE EXISTING IN CHLOROPLASTS

Two forms of aldolase, i.e. the membrane-bound form (M) and the stromal form (S), were found in the chloroplasts of rice, wheat, soybean, tobacco and spinach. Both the total activity of this enzyme in chloroplasts and the ratio between these two forms varied With the developmental stages of the plant. In rice, for example, the relative activity of the stromal aldolase Was much higher in grain-filling stage (67% of the total activity) than in the seedling stage (46%), and the total activity of the former was about 5-fold of that of the latter.Membrane-bound aldolase could be solubilized from thylakoid membrane by treatment with detergents, either 0.10% Triton X-100 or 0.1%DOC, but Triton, a stronger detergent, was much more effective.These two forms of aldolase were purified from spinach chloroplast by ammonium sulfate (60% saturation) precipitation, the precipitate Was solubilized with polyethleneglycol-6000, analysed by ion exchange chromatography On DEAE-cellulose 32 and then separated by preparative electrophoresis on acrylamide gel. The purified preparations were proved to be homogeneous by disk electrophoresis. The molecular weight of the soluble aldolase determined by SDS gel electrophoresis was 108 KD and that of the membrane-bound form was 104 KD. Moreover, they showed the same immunochemical behaviour in double-diffusion reaction and had very similar amino acid composition.All these implied that both of them had high degree of structural similarity, they were most Probably thesame enzyme existing in different forms. This phenomenon might be involved in the regulation of photosynthetic carbon reduction cycle and in the export of photosynthate from source to sink.