Stromal reactions

Genetic Changes in Colon Cancer Progression and Stromal Reactions... 

In retrospect, the attempts to inhibit MMPs failed because they cleave not only ECM components, but also many other proteins including growth factorbinding proteins, cytokine precursors, chemokines, etc. [40]. The proteolysis of these MMP substrates results in the release and/or activation of secreted factors that stimulate stomal cell infiltration and proliferation. Therefore, it is not surprising that systemic and prolonged inhibition of MMP activities causes aberrant immune responses and other stromal reactions. The ineffectiveness of MMP inhibitors may be explained partly by the recent findings that cancer stromal cells have non-MMP proteases that degrade ECM, such as cathepsins [16] and uPARAP/Endo 180 [8],... 

FIGURE 22.20 The molecular architecture of PSI. PsaA and PsaB constitute the reaction center dimer, an integral membrane complex P700 is located at the lumenal side of this dimer. PsaC, which bears Fe-S centers and Fb, and PsaD, the interaction site for ferre-doxin, are on the stromal side of the thylakoid membrane. PsaF, which provides the plasto-cyaiiin interaction site, is on the lumenal side. (Adapted from Golbeck, J. H., 1992. Amiual Review of Plant Physiology and. Plant Molecular Biology 43 293-324.)... 

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. 

The most frequent adverse reactions to trifluridine administration are transient burning or stinging and palpebral edema. Other adverse reactions include superficial punctate keratopathy, epithelial keratopathy, hypersensitivity, stromal edema, irritation, keratitis sicca, hyperemia, and increased intraocular pressure. 

Iron-sulfur clusters are important co-factors in electron-transfer. Type I reaction centres contain [4Fe-4S] clusters as final electron acceptors mediating ET to soluble electron carriers like ferredoxin or flavodoxin (reviewed in references 188, 224, 314, 315) In PS I three clusters (F FA and FB) have been clearly identified and spectroscopically characterized. The PsaA and PsaB subunits carry most of the ET cofactors in PS I.18178-316 Each of them provides two Cys ligands to the binding site of the interpolypeptide [4Fe-4S] cluster Fx. This binding site is identical on both core PS I subunits.317 Both [4Fe-4S] clusters FA and Fb are bound to the PS I stromal subunit PsaC. It contains two identical [4Fe-4S] consensus binding sites CxxCxxCxxxCP (C = cysteine, P = proline). 

Zang et al. developed a peptide-based polyurethane scaffold for tissue engineering. LDI was reacted with glycerol and upon reaction with water produced a porous sponge due to liberation of CO2. Initial cell growth studies with rabbit bone marrow stromal cells showed that the polymer supported cell growth. 

FIGURE 20-17 Source of ATP and NADPH. ATP and NADPH produced by the light reactions are essential substrates for the reduction of C02. The photosynthetic reactions that produce ATP and NADPH are accompanied by movement of protons (red) from the stroma into the thylakoid, creating alkaline conditions in the stroma. Magnesium ions pass from the thylakoid into the stroma, increasing the stromal [Mg2+],... 

The electron acceptors on the reducing side of photosystem II resemble those of purple bacterial reaction centers. The acceptor that removes an electron from P680 is a molecule of pheophytin a. The second and third acceptors are plastoquinones (see fig. 15.10). As in bacterial reaction centers, electrons move one at a time from the first quinone to the second. When the second quinone becomes doubly reduced, it picks up protons from the stromal side of the thylakoid membrane and dissociates from the reaction center. 

The protein complex that carries out this reaction is called coupling factor or, more accurately, ATP synthase. ATP synthase is a complex of several proteins, shaped like a mushroom, with the cap on the stromal side of the thylakoid disc and the stalk going through the thylakoid... 

The chlorophyll-protein complexes are oriented in the lamellar membranes in such a way that the electron transfer steps at the reaction centers lead to an outward movement of electrons. For instance, the electron donated by Photosystem II moves from the lumen side to the stromal side of a thylakoid (see Figs. 1-10 and 5-19). The electron that is donated back to the trap chi (Pgg0) comes from H20, leading to the evolution of 02 by Photosystem II (Eq. 5.8). The 02 and the H+ from this reaction are released inside the thylakoid (Fig. 5-19). Because 02 is a small neutral molecule, it readily diffuses out across the lamellar membranes into the chloroplast stroma. However, the proton (H+) carries a charge and hence has a low partition coefficient (Chapter 1, Section 1.4A) for the membrane, so it does not readily move out of the thylakoid lumen. 

Figure 5-19. Schematic representation of reactions occurring at the photosystems and certain electron transfer components, emphasizing the vectorial or unidirectional flows developed in the thylakoids of a chloroplast. Outwardly directed election movements occur in the two photosystems (PS I and PS II), where the election donors are on the inner side of the membrane and the election acceptors are on the outer side. Light-harvesting complexes (LHC) act as antennae for these photosystems. The plastoquinone pool (PQ) and the Cyt b(f complex occur in the membrane, whereas plastocyanin (PC) occurs on the lumen side and ferredoxin-NADP+ oxidoreductase (FNR), which catalyzes electron flow from ferredoxin (FD) to NADP+, occurs on the stromal side of the thylakoids. Protons (H+) are produced in the lumen by the oxidation of water and also are transported into the lumen accompanying electron (e ) movement along the electron transfer chain.

Coupling between the H+ movements across the thylakoid membranes associated with electron flow and ATP formation occurs via a coupling factor known as an ATP synthetase, which is usually referred to as ATP synthase but also as an ATPase (because it can catalyze the reverse reaction leading to ATP hydrolysis). As illustrated in Figure 6-5, the ATP synthase has two components (1) a five-protein factor that occurs on the stromal side of a thylakoid, which can bind ADP, Pj, and ATP (labeled CFX in Fig. 6-5) and (2) a four-protein factor that is hydrophobic and hence occurs in the thylakoid membrane, through which H+ can pass (labeled CF0).5... 

Not all terpene synthases catalyse complex reactions. Isoprene synthase converts DMAPP to the hemiterpene (G5), isoprene (Fig. 5.1), a comparatively simple process involving the ionization of the diphosphate group, followed by double-bond migration and proton elimination (Silver and Fall, 1991). Present in chloroplasts in both stromal and thylakoid-bound forms, isoprene synthase is a homodimer that differs from other terpene synthases in many properties, such as subunit architecture, optimum pH and kinetic parameters... 

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