Membranes thylakoid, protein-based

Conversely, the core comp lex of PSI contains about 95 Chi a molecules [Glick and Melis 1988]. Since PSI in the Chi Mess mutant contains 246 Chi a molecules, it follows that about 150 Chi a molecules must be associated with LHC-I proteins. Based on the assumption of 10 Chi molecules per Lhca protein in PSI [Thornber et al. 1988], we estimated that about 15 LHC-I proteins must be assembled and functionally associated with PSI in the absence of Chi b. Consistent with these conclusions are the western blot results with polyclonal LHC antibodies (Fig 5) which showed the presence of significant amounts of LHC proteins in thylakoid membranes isolated from Chi Mess cells. 

G protein a membrane-bound protein that mediates the action of adenylate cyclase (24.3) grana bodies within tlie chloroplast that contain the thylakoid disks, the site of photosynthesis (22.1) guanine one of the purine bases found in nucleic acids (9.2)... 

The protons, now at 1,000-fold higher concentration in the thylakoid lumen than in the surrounding stroma, return across the thylakoid membrane from lumen to stroma and produce the chemical energy ATP by means of the protein-based machine ATP synthase, briefly considered below and in some detail in Chapter 8. 

Protein-based Machines in the Thylakoid and Inner Mitochondrial Membranes... 

A flow of electrons in a series of cell membrane-associated oxidation and reduction cycles provides the energy source in the energyconverting thylakoid membranes of plants and inner mitochondrial membranes of plants and animals. In the process of this electron flow, membrane proteins pump protons across a cell membrane to increase the concentration of protons on one side of the membrane (to be considered in Chapter 8). Another protein-based machine uses the high concentration of protons on one side of a cell membrane to drive the formation of ATP as the protons pass to the low concentration side of the membrane (also to be considered in Chapter 8). 

In 1963, Shin et al. (1) first isolated ferredoxin-NADP reductase (FNR, EC. 1.18.1.2) in crystalline form from spinach and demonstrated that the crystallized enzyme reduced NADP when it was added back together with ferredoxin to illuminated chloroplasts from which built-in FNR had been removed. In this experiment, however, a very large excess of crystallized FNR was required to restore the original activity. This requirement of excess FNR indicates that membrane-bound FNR is more functional in the NADP photoreduction than the FNR added in a soluble state. So our recent interest has been focused on the structure and function of membrane-bound FNR. We have found that two molecules of a small form of FNR, FNR-S, was connected with a new thylakoid protein, connectein, to form a large form of FNR, FNR-L. The FNR-L was anchored on the surface of thylakoids via a base protein to constitute a ferredoxin-NADP reductase complex. 

Figure 2.12. Overall structure of the dimer cytochrome h/, as measured by X-ray scattering for the thermophilic cyanobacteriiun Mastigocladus laminosus. Its position relative to the thylakoid membrane is indicated in Fig. 2.14. Resolution 0.3 nm. Based on Protein Data Bank ID 1UM3 (Kurisu et al, 2003).

Great attention has been paid to the application of thylakoid membranes and photosynthetic microorganisms in environmental pollution control. The biorecognition system based on the binding of certain herbicides to the photosynthetic reaction center of plants and microorganisms seems to be the most direa and simple method for herbicide detection. These systems used as sensor s recognition elements allow the detection of a broad range of herbicides. Unfortunately, their stability and sensitivity are insufficient in the most cases. From this point of view, the DI protein, which binds specifically... 

Innes and Brudvig [8] suggested a structural model for the location of d" " in PS II based on the data with Dy-EDTA. They stated that Dy-HEDTA caused the same effect as Dy-EDTA , which is contradictory to our results presented here. The reason for the discrepancy is not clear, but it may come from the different intactness of the thylakoid membranes. In their model of PS II, D locates near the middle of the membrane. This seems to be unexpected from the PS-II structure deduced from the X-ray structure of the bacterial reaction center and the sequence homology of the D2 protein in PS II with the M subunit of the bacterial reaction center [2,10]. Our estimation of the location of D (Table 2) is in good agreement with the proposed structure of PS II. 

On the basis of X-ray diffraction studies, the ultrastructure of chloroplast membrane has been analyzed by Kreutz - s, and the subject reviewed by him. Using the freeze-etching technique, Muehlethaler has suggested a picture for the thylakoid membrane based upon the bimolecular leaflet model. The salient feature in all these proposed models lies in their oriented bilayer lipid core, onto which other important cellular constituents, such as proteins and pigments, may interact through either ionic or van der Waals attraction, or both. Muehlethaler s interpretation is of special interest, in view of the experiments using the pigmented... 

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