Proton pump, bacteriorhodopsin

In this paper, we will describe one of examples, where artificial archaeal glycolipids are applied to the construction of nano-devices containing energy-conversion membrane proteins, by employing the phytanyl-chained glycolipid we have recently developed, i.e., l,3-di-o-phytanyl-2-o- ((3-D-maltotriosyl) glycerol (Mab (Phyt)2, Fig. 1) [16,17] and natural proton pump, bacteriorhodopsin (BR) derived from purple membranes of the extremely halophilic archaeon Halobacterium salinarium S9 [18],... 

Some results. Rapid kinetic methods have revealed that enzymes often combine with substrates extremely quickly,60 with values of k] in Eq. 9-14 falling in the range of 106 to 108 M 1 s . Helix-coil transitions of polypeptides have relaxation times of about 10-8 s, but renaturation of a denatured protein may be much slower. The first detectable structural change in the vitamin A-based chromophore of the light-operated proton pump bacteriorhodopsin occurs in - 5 x 10 8 s, while a proton is pumped through the membrane in... 

Another unique property of at least some of the halobacteria is the ability to grow phototrophically by employing the light-driven proton pump bacteriorhodopsin. The proton gradient that is produced is used directly to generate ATP (Hartmann et al., 1980 Oesterhelt and Kripphal, 1983). Photoassimilation of CO2 by halobacteria was shown by Danon and Caplan (1977) and Oren (1983). In vivo C02 fixation was demonstrated by Javor (1988) and the existence of the enzyme ribulose-bisphosphate carboxylase activity in several halobacteria was shown by Altekar and Rajagopalan (1990). 

Many of the early genetic studies were done on H. halobium and its related strains. The popularity of these strains stemmed from the fact that several interesting spontaneous mutations could be readily detected. Among the most characterized mutations are those that affect the production of the protein part of the purple membrane, the heavily studied light-driven proton pump bacteriorhodopsin. Spontaneous mutations occur at a frequency of lO 4. Analysis of these mutations showed that in almost every case a foreign DNA sequence was introduced into the bacterioopsin (bop) structural gene or into sequences surrounding it. 

Lanyi, J. K. (1998). Understanding structure and function in the light-driven proton pump bacteriorhodopsin./ Struct. Biol. 124, 164—178. 

Furthermore, many carotenoid metabolites exist that have distinct functions. One such example shown in Fig. 3 is retinal, the chromophore of visual pigments (rhodopsins) and the light-driven proton pump, bacteriorhodopsin. Other examples are the plant hormone, abscisic acid, or volatile compounds that contribute to the fragrance of roses, for example. 

The light-driven proton pump, bacteriorhodopsin (bR), is found in the purple membrane of Halobacterium halobium (24-26). 

A crucially important finding is that submitochon-drial particles or vesicles from broken chloroplasts will synthesize ATP from ADP and Pj, when an artificial pH gradient is imposed. Isolated purified FjEg ATPase from a thermophilic Bacillus has been coreconstituted into liposomes with the light-driven proton pump bacteriorhodopsin (Chapter 23). Illumination induced ATP synthesis. These observations support Mitchell s proposal that the ATP synthase is both spatially separate from the electron carriers in the membrane and utilizes the protonmotive force to make ATP. Thus, the passage of protons from the outside of the mitochondria back in through the ATP synthase induces the formation of ATP. What is the stoichiometry of this process ... 

In further membrane studies, the surface of Halobacterium salinarum was investigated in order to visualize the distribution of retinal-free and retinal-containing membrane domains (see Figure 11.12) [108]. Therein, the resonantly enhanced retinal moiety was used as a marker for the light-driven, proton-pump bacteriorhodopsin. In the first step, isolated purple membrane (PM) patches were characterized. In experiments on isolated PM patches, the sites of the retinal... 

Further examples for the use of solid-state NMR to study 7-TM proteins include the light-activated proton pump bacteriorhodopsin which could be studied in detail in its native environment, the purple membrane. Valuable high-resolution insights into the structure of the functional core - in particular the configuration of the covalently bound retinal at different states in the photocycle - could be obtained [176-180]. 

---