Borkhsenious ON, Mason CB, Moroney JV
Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Plant Physiol. 1998 Apr;116(4):1585-91. doi: 10.1104/pp.116.4.1585.
The pyrenoid is a proteinaceous structure found in the chloroplast of most unicellular algae. Various studies indicate that ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) is present in the pyrenoid, although the fraction of Rubisco localized there remains controversial. Estimates of the amount of Rubisco in the pyrenoid of Chlamydomonas reinhardtii range from 5% to nearly 100%. Using immunolocalization, the amount of Rubisco localized to the pyrenoid or to the chloroplast stroma was estimated for C. reinhardtii cells grown under different conditions. It was observed that the amount of Rubisco in the pyrenoid varied with growth condition; about 40% was in the pyrenoid when the cells were grown under elevated CO2 and about 90% with ambient CO2. In addition, it is likely that pyrenoidal Rubisco is active in CO2 fixation because in vitro activity measurements showed that most of the Rubisco must be active to account for CO2-fixation rates observed in whole cells. These results are consistent with the idea that the pyrenoid is the site of CO2 fixation in C. reinhardtii and other unicellular algae containing CO2-concentrating mechanisms.
蛋白核是一种存在于大多数单细胞藻类叶绿体中的蛋白质结构。各种研究表明，核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）存在于蛋白核中，尽管定位于此的Rubisco比例仍存在争议。莱茵衣藻蛋白核中Rubisco含量的估计值在5%到近100%之间。利用免疫定位法，对在不同条件下生长的莱茵衣藻细胞中定位于蛋白核或叶绿体基质的Rubisco量进行了估计。据观察，蛋白核中Rubisco的量随生长条件而变化；当细胞在高浓度CO2条件下生长时，约40%的Rubisco在蛋白核中，而在环境CO2条件下约为90%。此外，蛋白核中的Rubisco可能在CO2固定中具有活性，因为体外活性测量表明，大部分Rubisco必须具有活性才能解释在整个细胞中观察到的CO2固定速率。这些结果与蛋白核是莱茵衣藻和其他具有CO2浓缩机制的单细胞藻类中CO2固定位点的观点一致。
