Newly isolated archaerhodopsin from a strain of Chinese halobacteria and its proton pumping behavior

A strain of extremely salt-loving halobacteria Halobacterium species xz515 from a salt lake in Tibet was isolated. SBS-polyacrylamide gel electrophore sis shows that there is only one protein on claret membrane, which is the s ame membrane fraction as purple membrane from Halobacterium salinarum, with a molecular weight close to bacteriorhodopsin (br). The purified retinal c ontaining protein from xz515 has an absorption peak at around 550 nm. These facts indicate that it is a br-like protein. The partial sequence determin ation [H. Wang et al., Chin. Sci. Bull., 45 (2000)] shows that this br-like protein belongs to the archaerhodopsin family. The measurements of light-i nduced medium pH change in intact cells and cell envelope vesicles of xz515 suggest that this type of archaerhodopsin has a proton pumping function. H owever, the study about the dynamics of pumped protons across the membrane reveal that the proton release and proton uptake is in reverse order compar ed to br. The probable reason, attributing to regulating the rate of proton release is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.