Lumen side

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 thylakoid membrane is asymmetrically organized, or sided, like the mitochondrial membrane. It also shares the property of being a barrier to the passive diffusion of H ions. Photosynthetic electron transport thus establishes an electrochemical gradient, or proton-motive force, across the thylakoid membrane with the interior, or lumen, side accumulating H ions relative to the stroma of the chloroplast. Like oxidative phosphorylation, the mechanism of photophosphorylation is chemiosmotic. 

Figure 6, Polarized epithelial cells in culture. Epithelial cells in culture possess an apical surface with microvilli that faces the tissue culture medium (equivalent to the lumenal side of the cells in vivo), and a basolateral surface that faces the tissue culture dish (equivalent to the blood side of the cells in vivo).

PS1 The PS 1-prep, introduced in this communication is the first reported with a polyhistidine tag fused to the N-terminus of the PsaF subunit. This construct was possible due to the fact that cyanobacterial PsaF-deletion mutants show no impact on photoautotrophic growth - in contrast to Chlamydomonas reinhardtii, where inactivation of PsaF results in a severe reduction of electron transfer from plastocyanin to PS 1 [Hippier et al. 1997], Also, the N-terminus of the F-subunit which was decorated by the tag is located towards the lumen side which enables an attachment of the isolated PS1 with the lumen-exposed /donor-side to the electrode surface in our hydrogen-producing device. 

The atherosclerotic plaque consists, on the lumen side, of a layer of connective tissue containing smooth muscle cells and macrophages covering a deeper layer of macrophages containing so much hpid that they are known as foam cells due to their microscopic appearance. This layer also contains a varying amount of cell debris and extracellular lipid. Outside it, there is often a region of proliferated smooth muscle cells. 

Synthesis. The synthases are present at the endomembrane system of the cell and have been isolated on membrane fractions prepared from the cells (5,6). The nucleoside diphosphate sugars which are used by the synthases are formed in the cytoplasm, and usually the epimerases and the other enzymes (e.g., dehydrogenases and decarboxylases) which interconvert them are also soluble and probably occur in the cytoplasm (14). Nevertheless some epimerases are membrane bound and this may be important for the regulation of the synthases which use the different epimers in a heteropolysaccharide. This is especially significant because the availability of the donor compounds at the site of the transglycosylases (the synthases) is of obvious importance for control of the synthesis. The synthases are located at the lumen side of the membrane and the nucleoside diphosphate sugars must therefore cross the membrane in order to take part in the reaction. Modulation of this transport mechanism is an obvious point for the control not only for the rate of synthesis but for the type of synthesis which occurs in the particular lumen of the membrane system. Obviously the synthase cannot function unless the donor molecule is transported to its active site and the transporters may only be present at certain regions within the endomembrane system. It has been observed that when intact cells are fed radioactive monosaccharides which will form and label polysaccharides, these cannot always be found at all the membrane sites within the cell where the synthase activities are known to occur (15). A possible reason for this difference may be the selection of precursors by the transport mechanism. 

It is likely that in addition to the synthases and epimerases there is also present at the membrane in close proximity to these, transporter systems for the transfer of the nucleoside diphosphate donor compounds to the transglycosylases situated on the lumen side of the membrane. 

A relatively small minority of APP molecules enter the p-secretase pathway in which p-secretase cleaves APP and releases a soluble fragment, sAPPp. The C-terminal membrane-bound C99 peptide is then cleaved by y-secretase within the transmembrane domain, and two major isoforms of 40 and 42 amino acid lengths with different C-termini, Ap40 and Ap42, are generated. Based on the amino acid sequence, p-secretase is predicted to be a type I transmembrane protein with the active site on the lumenal side of... 

This Mg2+-activated enzyme is found on the lumenal side of the endoplasmic reticulum of hepatocytes and renal cells (see Fig. 15-6). Muscle and brain tissue do not contain this enzyme and so cannot carry out gluconeogenesis. Glucose produced by gluconeogenesis in the liver or kidney or ingested in the diet is delivered to brain and muscle through the bloodstream. 

The development of COX-2-specific inhibitors has been helped immensely by knowledge of the detailed three-dimensional structures of COX-1 and COX-2 (Fig. 1). Both proteins are homodimers. Each monomer (A/, 70,000) has an amphipathic domain that penetrates but does not span the ER this anchors the enzyme on the lumenal side of the ER (a very unusual topology—generally the hydrophobic regions of integral membrane proteins span the entire bilayer). Both catalytic sites are on the globular domain protruding into the ER lumen. 

Xylanase. The sprucewood holocellulose treated with xylanase shows, in general, a mild attack especially in the wall region at the lumen-wall boundary. A progressive dissolution of substances can also be detected from Si into the adjacent S2 as well as from the lumen side into the secondary wall (Figure 8). This decrustation appears to be not very extensive in total, inasmuch as the affected wall areas are proportionally few. Compared with the loss of opacity in the lumen-wall boundary, the Si is not affected to such a great extent. The corners of the tracheids exhibit a high transparency, obviously due to removal of substances, as compared to the remainder of the middle lamella region. 

Figure 1. PC2 channels inhibited by Gd3+. The top panel shows currents obtained from PC2 incorporated into a bilayer. This is a control trace showing Cs+ current measured at 15 mV transmembrane potential. The solid and broken lines to the right of the traces indicate the closed and open states, respectively. The second and third traces show currents after the addition of Gd3+. The bottom panel shows the concentration dependence of the block by Gd3+, circles when added to the cytoplasmic side, squares when added to the lumenal side. The Kd is 206 pM Gd3+ only blocks when added to the cytoplasmic side. Modified from (Anyatonwu and Ehrlich 2005)...

If we consider a gas-liquid transfer for the species i in a hollow-fiber module with the liquid phase in the shell side and the gas phase in the lumen side of hydrophobic membranes, the interface is established at the outer diameter of the fibers and the overall mass-transfer coefficient can be calculated by [1] ... 

Figure 21.13 Emulsification devices where the membrane is immersed in a stirred vessel containing the continuous phase. Transmembrane pressure applied from (a) external or shell side, and (b) internal or lumen side.

Interestingly, it appears that it is easier to induce the formation of a helical hairpin with the tight turn on the lumenal side of the ER membrane than one with the opposite orientation (cytoplasmic turn) i.e., whereas a single Pro is enough to convert the 40-residues long poly (Leu) stretch to a helical hairpin with a lumenal turn, three consecutive prolines are needed for a helical hairpin with a cytoplasmic turn to form (Saaf et al., 2000) (Fig. 2B). If one only considers simple protein—lipid interactions there is no obvious thermodynamic reason why this should be so instead, we favor the view that this reflects a constraint on helical hairpin structure imposed by the Sec machinery. 

Advances in the study of photosynthetic manganese and the water oxidation complex have been accelerated by the development of techniques for the isolation of photosystem II particles by Triton-X and/or digitonin treatment of thylakoid membranes (188,189). Freeze-fracture electron microscopy indicates the particles are highly purified membrane fragments almost entirely devoid of photosystem I components (190). The lumenal side of the photosystem II membrane is exposed, allowing direct access to the water oxidation enzyme complex. These PSII preparations contain four atoms of manganese per PSII reaction center and possess large amounts of 02 activity (191, 192). 

---