蓝藻Anabaena sp.PCC7120羧体碳酸酐酶的鉴定

CHARACTERIZATION OF CARBOXYSOMAL CARBONIC ANHYDRASE IN CYANOBACTERIUM ANABAENA SP. PCC7120

在丝状蓝藻AnabaenaspPCC7120细胞租提液的碳酸酥酶（CA）分析中，发现了两种形式的CA活性．高CO2下生长的细胞，在35pmol／LEZ（Ethoxyzoamide，碳酸醉酶的抑制剂）存在的情况下，CA总活性的85％左右被抑制，其半抑制浓度I50为7.4μmol／L；随着EZ浓度的继续增加，CA活性在EZ浓度达到约150μmol／L处出现了第二个抑制峰，在250μmol／L处抑制程度达到最大，使CA总活性的15％被抑制，其半抑制浓度I50为190μmol／L．在空气条件下生长的细胞中也出现了CA的两个抑制峰：低I50为6μmol／L，高I50为120μmol／L．对核体的分离及体外测试表明，在波体制备物中的CA活性只有一个EZ的抑制峰，而且在EZ浓度达到35μmol／L，正如所期望的那样，该CA活性全部被抑制．其半抑制浓度150为5．2μmol／L左右．这个值跟空气或高CO2条件下生长的细胞粗提物中的低I50（6μmol／L或7．4μmol／L）十分相似．说明低浓度的EZ可以特异性地抑制定位于校体的CA活性．另外一种形式的CA，具有高I50（120－190μmol／L），约占CA总活性的15－20％，则有可能定位于细胞质膜．

In this work, two types of carbonic anhydrase were fund in the crude extracts of Anabaena sp. strain PCC712. In high CO2-grown cells, c. a. 85 % total CA activity was inhibited by 35μmol/LEZ, and its half inhibited concentration (I50) was 7. 4μmol/L; With the elevation of EZ levels, the second peak of inhibition for CA appeared when the concentration f EZ reached 150pmol/L. The remaining 15 % CA activity was cmpletely inhibited in the presence of 250μmol/L EZ, and its I50 was 190μmol/L. In air-grown cells of Anabaena sp. PCC712, the similar tw peaks of inhibition for CA also appeared: the lw I50 was 6μmol/L and the high I50 was 12pmol/L. Isolatin f carboxysomes and the assays in vitro showed, that only one inhibition peak for CA appeared in the preparations of carbxysomes.As expected, the overall CA activity was inhibited in the presence of 35μmol/L EZ, with I50of 5. 2pmol/L, which was very similar to the low I50 value in the crude extracts of air-grown cells and high CO2-grown cells. The results indicated that low levels of EZ specificaIly inhibited the CA lcated within carboxysomes. The other types of CA, which had a high I50(120-190μmol/L) and contained c. a. 15 - 20 % of the ttal CA activity of the crude extracts,probably located in the cell membrane.