CARBONIC-ANHYDRASE ACTIVITY ASSOCIATED WITH THE CYANOBACTERIUM SYNECHOCOCCUS PCC7942
CARBONIC-ANHYDRASE ACTIVITY ASSOCIATED WITH THE CYANOBACTERIUM SYNECHOCOCCUS PCC7942
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DOI：
10.1104/pp.89.1.51
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发表时间：
1989-01-01
期刊：
影响因子：
7.4
通讯作者：
PRICE, GD
中科院分区：
文献类型：
--
作者：
BADGER, MR;PRICE, GD
在高（1%CO2）和低溶解无机碳（Ci）（30-50微升/升CO2）下生长的聚球藻PCC 7942的完整细胞和粗匀浆具有碳酸酐酶（CA）样活性，这使得它们能够催化18 O从CO2交换为H2O。使用与具有膜入口系统的比色皿耦合的质谱仪研究该活性。发现完整的高和低Ci细胞含有CA活性，通过优先渗透CO2的膜与培养基分离。这种活性在光照下最明显，其中18 O标记的CO2物质被细胞吸收，但流出的CO2已经失去了大部分标记水。在黑暗中，低Ci细胞催化耗尽的18 O富集的CO2和这种活性抑制乙氧唑胺和2-（三氟甲氧基）羰基氰。这可能通过Ci泵的共同抑制而发生，并且Ci泵被提议作为18 O交换的潜在位点。CA活性在两种细胞类型的匀浆中是可测量的，但在低Ci细胞中高5至10倍。这是抑制乙氧基唑胺与50至100微摩尔的低和高Ci细胞。大部分的内部CA活性在性质上似乎是可造粒的。这种pelletability增加的Mg 2+的存在下，以类似的方式，核酮糖二磷酸羧化酶加氧酶活性和叶绿素（类囊体），可能是非特异性聚集的结果。粗匀浆在蔗糖梯度上的分离与CA和二磷酸核酮糖羧化酶-加氧酶活性可能与相同的可造粒级分相关的概念一致。然而，我们不能明确地确定CA位于羧基体内。蔗糖梯度显示存在单独的可溶性和可沉淀的CA活性。这可能是由于存在不同形式的酶，或者可能是由于在提取过程中不稳定的相同的可沉淀缔合物。
Intact cells and crude homogenates at high (1% CO2) and low dissolved inorganic carbon (Ci) (30-50 microliters per liter of CO2) grown Synechococcus PCC7942 have carbonic anhydrase (CA)-like activity, which enables them to catalyze the exchange of 18O from CO2 to H2O. This activity was studied using a mass spectrometer coupled to a cuvette with a membrane inlet system. Intact high and low Ci cells were found to contain CA activity, separated from the medium by a membrane which is preferentially permeable to CO2. This activity is most apparent in the light, where 18O-labeled CO2 species are being taken up by the cells but the effluxing CO2 has lost most of its label to water. In the dark, low Ci cells catalyze the depletion of the 18O enrichment of CO2 and this activity is inhibited by both ethoxyzolamide and 2-(trifluoromethoxy)carbonyl cyanide. This may occur via a common inhibition of the Ci pump and the Ci pump is proposed as a potential site for the exchange of 18O. CA activity was measurable in homogenates of both cell types but was 5- to 10-fold higher in low Ci cells. This was inhibited by ethoxyzolamide with an I50 of 50 to 100 micromolar in both low and high Ci cells. A large proportion of the internal CA activity appears to be pelletable in nature. This pelletability is increased by the presence of Mg2+ in a manner similar to that of ribulose bisphosphate carboxylase-oxgenase activity and chlorophyll (thylakoids) and may be the result of nonspecific aggregation. Separation of crude homogenates on sucrose gradients is consistent with the notion that CA and ribulose bisphosphate carboxylase-oxygenase activity may be associated with the same pelletable fraction. However, we cannot unequivocally establish that CA is located within the carboxysome. the sucrose gradients show the presence of separate soluble and pelletable CA activity. This may be due to the presence of separate forms of the enzyme or may arise from the same pelletable association which is unstable during extraction.