Helmerhorst Eva J, Stan Maria, Murphy Michael P, Sherman Fred, Oppenheim Frank G
Department of Periodontology and Oral Biology, Goldman School of Dental Medicine, Boston University, 700 Albany Street W201, Boston, MA 02118, USA.
Mitochondrion. 2005 Jun;5(3):200-11. doi: 10.1016/j.mito.2005.04.001.
The opportunistic oral pathogen Candida albicans expresses a cyanide-insensitive alternative oxidase (AOX) upon exposure to respiratory inhibitors that act downstream from coenzyme Q, and upon ageing of cells. To investigate whether the conventional pathway is retained when the alternative pathway is induced, cells were grown in the presence of sodium cyanide, a reversible inhibitor of cytochrome oxidase. AOX expression was monitored by Western blotting and the presence of cytochromes associated with complexes III and IV of the conventional pathway was monitored by recording spectra between 500 and 650 nm at 77K. The activities of complexes III and IV were determined in polarographic and enzyme-kinetic experiments using specific respiratory substrates and inhibitors. Results indicated that complexes III and IV are constitutively expressed and are functional in cells expressing AOX. Furthermore, the enzymatic activities of complexes III and IV were similar in mitochondrial preparations from cells grown with or without cyanide. We next investigated whether both pathways are simultaneously available for electron transfer from the Q pool to molecular oxygen. Respiration was virtually completely inhibited by the combination of cyanide and salicyl hydroxamic acid (SHAM) or antimycin A and SHAM, but only partly inhibited by either of these inhibitors alone. This indicates that electrons can in principle flow either through the conventional or the alternative respiratory pathway. The availability of two electron pathways in C. albicans and the potential use of either pathway endows this pleomorphic fungus with another level at which it can rapidly adjust to altered environmental conditions.
机会性口腔病原体白色念珠菌在暴露于作用于辅酶Q下游的呼吸抑制剂时以及细胞老化时会表达一种对氰化物不敏感的交替氧化酶（AOX）。为了研究当诱导交替途径时传统途径是否保留，细胞在细胞色素氧化酶的可逆抑制剂氰化钠存在的情况下生长。通过蛋白质印迹法监测AOX的表达，并通过在77K下记录500至650nm之间的光谱来监测与传统途径的复合物III和IV相关的细胞色素的存在。使用特定的呼吸底物和抑制剂，在极谱和酶动力学实验中测定复合物III和IV的活性。结果表明复合物III和IV是组成型表达的，并且在表达AOX的细胞中具有功能。此外，在有或没有氰化物生长的细胞的线粒体制备物中，复合物III和IV的酶活性相似。接下来，我们研究了两条途径是否同时可用于从Q池到分子氧的电子传递。氰化物和水杨基羟肟酸（SHAM）或抗霉素A和SHAM的组合几乎完全抑制了呼吸，但单独使用这些抑制剂中的任何一种仅部分抑制了呼吸。这表明电子原则上可以通过传统呼吸途径或交替呼吸途径流动。白色念珠菌中两条电子途径的可用性以及任何一条途径的潜在用途赋予了这种多形真菌另一个层面，使其能够快速适应变化的环境条件。
