Galván A, Quesada A, Fernández E
Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias, Universidad de Córdoba, Spain.
J Biol Chem. 1996 Jan 26;271(4):2088-92. doi: 10.1074/jbc.271.4.2088.
Nitrate transport mutants from Chlamydomonas reinhardtii and strains derived from them upon transformation with plasmids containing the C. reinhardtii nar2/Nrt2;1 or nar2/Nrt2;2 genes have been used to study nitrate and nitrite transport systems. Mutants lacking nitrate assimilation clustered genes showed a high affinity nitrite transporter activity (system 3), which was subject to ammonium inhibition and appeared to be independent of a functional nar2 gene. Transformants carrying nar2/Nrt2;2 recovered a high affinity nitrate transporter activity (system 2) and showed nitrite transport activities with properties similar to those in nonrecovered high affinity nitrate transporter activity (system 1) together with a considerably enhanced nitrite transport activity. Nitrite transport mediated by system 1 was very sensitive to inhibition by nitrate at microM concentrations. Results strongly suggest that three nitrate assimilation related high affinity transport systems operate in C. reinhardtii: one specific for nitrite, a second one encoded by nar2/Nrt2;2 specific for nitrate, and another one encoded by nar2/Nrt2;1, which is bispecific for these two anions.
莱茵衣藻的硝酸盐转运突变体以及用含有莱茵衣藻nar2/Nrt2;1或nar2/Nrt2;2基因的质粒转化后得到的菌株，已被用于研究硝酸盐和亚硝酸盐转运系统。缺乏硝酸盐同化相关簇基因的突变体表现出高亲和力亚硝酸盐转运活性（系统3），该活性受到铵的抑制，且似乎不依赖于功能性nar2基因。携带nar2/Nrt2;2的转化体恢复了高亲和力硝酸盐转运活性（系统2），并表现出与未恢复高亲和力硝酸盐转运活性（系统1）相似的亚硝酸盐转运活性，同时亚硝酸盐转运活性显著增强。系统1介导的亚硝酸盐转运对微摩尔浓度的硝酸盐抑制非常敏感。结果强烈表明，莱茵衣藻中存在三种与硝酸盐同化相关的高亲和力转运系统：一种对亚硝酸盐具有特异性，第二种由nar2/Nrt2;2编码，对硝酸盐具有特异性，另一种由nar2/Nrt2;1编码，对这两种阴离子具有双特异性。
