Membrane thylakold

The exploratory studies, as conducted, did not distinguish between effects Imposed on the stromal-associated CO2 fixation (Calvin cycle) reactions or on the light reactions associated with the thylakoids. Consequently, studies were conducted on light-induced electron transport and ATP synthesis associated with isolated spinach thylakold membranes. 

Figure 4. Postulated electron transport systems of a thylakold membrane.

Fig. 2. (A) SDS-electrophoretogram of the photosystem-l reaction center (B) A model for the subunit structure and function of the PS-I reaction center in the thylakold membrane (bottom) a tabulation of the detected subunits designated with Roman numerals and the corresponding PsaX designations and the molecular masses. Figure source Bengis and Nelson (1977) Subunit structure of ch/orop/asf photosystem i reaction center. J Biol Chem 252 4566,4568.

Chloroplasts contain a complex system of thylakold membranes In their Interiors. These membranes contain the pigments and enzymes that absorb light and produce ATP during photosynthesis. 

Stage 3 Synthesis of ATP Protons move down their concentration gradient from the thylakold lumen to the stroma through the FqFi complex (ATP synthase), which couples proton movement to the synthesis of ATP from ADP and Pj. The mechanism whereby chloroplast FqFi harnesses the proton-motive force to synthesize ATP is identical with that used by ATP synthase in the inner mitochondrial membrane and bacterial plasma membrane (see Figures 8-24 and 8-26). 

FqFi complexes in the thylakold membrane use the proton-motive force generated during linear electron flow to synthesize ATP on the stromal side of membrane. Thus this pathway yields both NADPH and ATP in the stroma of the chloroplast, where they are utilized for CO2 fixation. 

The splitting of H2Q, which provides the electrons for reduction of Peso in PSII, is catalyzed by a three-protein complex, the oxygen-evolving complex, located on the luminal surface of the thylakold membrane. The oxygen-evolving complex contains four manganese (Mn) ions as well as... 

FqFi ATPase/ATP synthase of mitochondrial Inner membrane, chloroplast thylakold, and bacterial plasma membrane... 

Benzoic acids generally seem to be formed In micro-compartments. After the first demonstration of phenylalanine ammonla-lyase (PAL) at thylakold membranes (3)... 

It is not unlikely that membrane conqplexes, too, function in the biosynthesis of plastoqulnone (see Fig. 1). A tyrosine-specific amino acid c cldase and the p-hydroxypyruvate oxygenase both could be localized at thylakoldal membranes of Lemna glbba grown under sterile conditions (9 Loffelhardt and Kindi, unpublished). 

With heterologous antibodies we Investigated the presence or absence of various PSII polypeptides In wlldtype and mutant S. 6803 cells (Table 1). The findings from this analysis reveal three aspects of particular Interest 1) Despite the lack of the D1 and D2 polypeptides several other Intrinsic PSII polypeptides could still accumulate in mutant thylakolds. 2) The intrinsic 22 kDa polypeptide, so far known only from PSII in plants [1], is present also in cyanobacteria and was retained in mutant thylakoids. 3) The extrinsic 33 kDa polypeptide was present and membrane-bound in mutant thylakoids. 

The loss of the Dl-protein raises several questions concerning the organization of PS II under photoinhibited conditions. These relate to ligation of cofactors, assembly of Intrinsic and extrinsic proteins, site and mechanism of repair. Here we have used different techniques i.e. Mn analysis, immunoblotting and thylakold membrane subfractionation to study In vitro the consequences of Dl-protein degradation on the organization of the PS II complex. 

Light-induced conformational change of thylakolds was widely studied in the 60 -70 s[l][2]. Recently, the curiosity to understand the regulatory process of photosynthesis in vivo[3] has led people to work on this topic again[4][5]. It has been demonstrated that the shrinkage of thylakolds is Induced by ApH and osmotic movement of weak organic acids across thylakoid membrane[2][6]. However, it... 

Fig. 3. Polypeptide profiles (tracks labelled a) and their autoradiograms (tracks labelled b) of thylakold membranes isolated from leaves grown in = p-orthophosphate and exposed to control, chill in high light (HL) and chill in low light (LL) treatments...

E. Shimoni, 0. Rav-Hon, I. Chad, V. Brumfeld, and Z. Reich, Three-dimensional organization of higher-plant chloroplast thylakold membranes revealed by electron tomography. Plant Cell, 17, 2580-2586... 

TAbLE 4. Distribution of newly-synthesized lipids, MGDG, and MGDG fatty acids between envelope and thylakold membranes during a chase... 

Goughian SJ and Schreiber U (1983) The differential effects of short time glutaraldehyde treatments on light induced thylakold membrane conformational changes,proton pumping and electron transport properties BiochimoBiophySoActa (submitted)... 

Thorne SW,Horvath 6,Kahn A and Boardman K (1975) Light-dependent absorption and selective scattering changes at 5l8nm in chloroplast thylakold membranes Proc Nat. Acad Sci. USA 72, 3858-3862. 

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