Halobacterium halobium activity

Animals cannot synthesize vitamin A-active compounds and necessary quantities are obtained by ingestion of vitamin A or by consumption of appropriate provitamin A compounds such as P-carotene. Carotenoids are manufactured exclusively by plants and photosynthetic bacteria. Until the discovery of vitamin A in the purple bacterium Halobacterium halobium in the 1970s, vitamin A was thought to be confined to only the animal kingdom (56). Table 4 Hsts RDA and U.S. RDA for vitamin A (67). 

A three-dimensional structure also has been elucidated for bacteriorhodopsin, an integral membrane protein of the halophilic (salt-loving) bacterium Halobacterium halobium. This protein has been studied intensively because of its remarkable activity as a light-driven proton pump (see chapter 14). It forms well-ordered arrays in two-dimensional sheets that can be studied by electron diffraction. Measurements of the diffraction patterns show clearly that bacteriorhodopsin has seven transmembrane helices (fig. 17.12). 

Bacteriorhodopsin, is a retinal-containing protein in the purple membrane of a halophilic, (salt-loving) archaebacterium, Halobacterium halobium, which pumps protons out of the cell on activation by light.The three-dimensional structure of bacteriorhodopsin resembles that of rhodopsin in the eye. 

Data are from references [89,91,92] and from Mikulik (personal communication) for Calderobacterium hydrogenophilum. Reverse gyrase activity has not been detected in moderately thermophilic and mesophilic eubacteria from the genera Bacillus and Thermus [89]. In all cells lacking reverse gyrase activity, except Halobacterium halobium, one can detect an ATP-independent relaxation activity. 

Natronobacterium pharaonis, an alkaliphilic halobacterium, contains a halorhodopsin as well, though at only 10% of the level of halobium hop. The activity of pharaonis halorhodopsin in vitro is not more alkali tolerant than is halobium hop their pH dependence is similar. Unlike halobium halorhodopsin, the pharadopsin hop transports nitrate as well as it does chloride [141]. The pharaonis hop gene was cloned by probing with the gene from Halobacterium halobium, and its identity was confirmed by comparison with partial peptide sequence obtained from the purified protein [142]. 

Similarly, chemotactic behaviour of bacteria is controlled by Ca . Mobile bacteria swim towards certain chemicals and away from others. Such bacteria can swim smoothly in a straight line or tumble, which results in random changes in direction. When heading towards repellents bacteria tumble more frequently to increase the probability of swimming away. Influx of Ca causes tumbling. Such behaviour has been found for Bacillus subtilis but apparently not for E. co/i. Calcium accelerates the swimming speed of Chlamydomonas reinhardii and regulates reverse motion in phototactically active Phormidium uncinatum and Halobacterium halobium. Phototaxis in H. halobium involves a methylation-demethylation process which is calcium dependent. Attractant stimuli raise the level of methylation of membrane proteins, while repellent stimuli cause demethylation and the enhanced opportunity for reversal of direction. Ca " " deactivates the methyl transferase and activates a methyl esterase. ... 

Another interesting example for severe hydration effects in relation to charge transfer is the purple membrane of Halobacterium halobium it acts as a photoelectret, producing at least semipermanent electric charges upon illumination this activity has been shown to be greatly affected by hydration. 

Moreover, the chromoprotein bacteriorhodopsin from Halobacterium halobium has been incorporated into liposomes of the polymerizable sulfolipid 61. Bacteriorhodopsin was found to be active as a light-driven proton pump in the polymerized liposomes... 

There are two ways in which membranes of diacetylenic lipids containing intrinsic membrane proteins can be obtained either proteins extracted from natural membranes with detergent can be reconstituted into synthetic diacetylenic phosphatidylcholines or the growth medium of micro-organisms incapable of synthesizing their own fatty acids can be enriched with diacetylenic fatty acid. In this laboratory, Ca2+-ATPase from sarcoplasmic reticulum and bacteriorhodopsin from the purple membrane of Halobacterium halobium have been reconstituted into diacetylenic phosphatidylcholines. Provided the more reactive mixed-chain lipids are used polymerisation can be achieved before the protein is denatured by the UV irradiation. Both proteins remain active within polymeric bilayers. 

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