Chloroplast membrane, inner

Like the Tom and Tim systems on mitochondrial outer and inner membranes, chloroplasts use the Toe and Tic systems on their outer and inner envelope membranes. Although there may not be a direct correspondence between both subunits, their functions for protein translocation appear quite similar. Thus, most of the sorting mechanisms within the envelope membranes are recognized as variations of the general sorting pathway to the stroma. 

Let us mention a little more about cytochrome c (cyt c). Cyt c is a protein known to exist in mitochondrial inner membranes, chloroplasts of plants, and bacteria [11]. Its functions are related to cell respiration [12] and cyt c, using its heme molecule, delivers an electron from cytochrome be 1 to cytochrome oxidase—two larger proteins both embedded in a membrane. Recently it was also found that cyt c is released when apoptosis occurs [13]. In this sense, cyt c governs the life and death of a cell. 

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

Characteristic of all chloroplasts, however, is the organization of the inner membrane system, the so-called thylakoid membrane. The thylakoid membrane... 

The marker enzymes used in this experiment are as follows vanadate-sensitive H+-ATPase (plasma membrane), nitrate-sensitive H+-ATPase or pyrophosphatase (tonoplast), TritonX-100 stimulated-UDPase or IDPase (Golgi complex), antimycin A-insensitive NADPH cytochrome c reductase (ER), and cytochrome c oxidase (mitochondria inner membrane). NADH cytochrome c reductase activity is found to be 10 times higher than NADPH cytochrome c reductase activity. Chlorophyll content can be measured as the chloroplast marker. The chlorophyll content is calculated by the following equation. Before measurement, auto zero is performed at 750 ran. 

Most of the arguments described in the sections on bacterial signal peptides and membrane proteins seem to be valid for the eukaryotic systems, as well as the translocation phenomena across the ER membrane (Sakaguchi, 1997). They seem to be also true for the translocation system across the mitochondrial inner membrane protein into the intermembrane space and the system across the thylakoid membrane in chloroplasts. Although the TAT-dependent pathway has not been found in the ER, it exists on the thylakoid membrane (and possibly on the inner membrane of mitochondria). 

Chloroplasts are a typical type of plastid that performs various metabolic reactions as well as photosynthesis. Their envelope consists of two membranes the outer envelope membrane and the inner membrane (Fig. 7). The space between these two membranes is called the intermembrane space, and the space enclosed by the inner envelope membrane is called the stroma. In addition, chloroplasts have another membrane system within the stroma the thylakoid membrane forms the lumen. Therefore, there are six different localization sites and, of course, multiple pathways to each site. Naturally, their sorting mechanisms are very complicated. 

In photosynthetic eukaryotic cells, both the light-de-pendent and the carbon-assimilation reactions take place in the chloroplasts (Fig. 19-38), membrane-bounded intracellular organelles that are variable in shape and generally a few micrometers in diameter. Like mitochondria, they are surrounded by two membranes, an outer membrane that is permeable to small molecules and ions, and an inner membrane that encloses the internal compartment. This compartment contains many flattened, membrane-surrounded vesicles or sacs, the thylakoids, usually arranged in stacks called grana (Fig. 19-38b). Embedded in the thylakoid membranes (commonly called lamellae) are the photosynthetic pigments and the enzyme complexes that carry out the light reactions and ATP synthesis. The stroma (the aqueous phase enclosed by the inner membrane) contains most of the enzymes required for the carbon-assimilation reactions. 

Ferrochelatase (protoheme ferro-lyase)401 403 inserts Fe2+ into protoporphyrin IX to form heme. The enzyme is found firmly bound to the inner membrane of mitochondria of animal cells, chloroplasts of plants, and chromatophores of bacteria. While Fe2+ is apparently the only metallic ion ordinarily inserted into a porphyrin, the Zn2+ protoporphyrin chelate accumulates in substantial amounts in yeast, and Cu2+-heme complexes are known (p. 843). Ferrochelatase, whose activity is stimulated by Ca2+, appears to be inhibited by lead ions, a fact that may account for some of the acute toxicity of lead.404... 

The photosynthetic process in green plants occurs in subcellular organelles called chloroplasts. These organelles resemble mitochondria they have two outer membranes and a folded inner membrane called the thy-lakoid. The apparatus for photosynthesis, including the chlorophyll reaction centers and electron carriers, is in the thylakoid membrane. The chemical reactions of the Calvin cycle take place in the stroma, the region around the thylakoid membrane. 

Algae are members of the plant kingdom and contain chloroplasts similar to those of higher plants, but prokaryotic photosynthetic organisms do not have chloroplasts. In prokaryotes, the photochemical reactions occur in the plasma membrane, which has extensive invaginations resembling the cristae of the mitochondrial inner membrane (fig. 15.3). Table 15.1 summarizes the main distinctions between the various types of photosynthetic organisms. 

Mitochondria, Gram negative bacteria, and chloroplasts have double envelopes of membranes. As we discussed, their inner membranes are impermeable to ions and polar molecules other than those that are transported by specific... 

Shimokawa e t a l. ( 16 ) examined the changes in chloroplast structure induced by ethylene in satsuma mandarin. Electron micrographs showed peel of ethylene-treated fruit had fewer chloroplasts and of smaller size. The inner membrane system of the chloroplasts was found to disintegrate prior to the breakdown of other cell structures. 

Reaction (14) and hence the overall rate of electron phototransfer across the membrane can be enhanced by providing additional excitation of the ZnTPPin molecules on the inner membrane surface. It could be done by virtue of energy transfer from some antenna collecting light and then transferring the excitation to the reaction centers , i.e. the ZnTPPin molecules embedded into the membrane this approach reproduces the action of a pull of the antenna chlorophyll in chloroplasts. In corresponding experiments (System 14 of Table 1) a water-soluble... 

Roise, D and Maduke, M. (1994) Import of a Mitochondrial Presequence into P. Denitrificans, FEBS Letters, 337, 9-13 Cavalier-Smith, T. (1987) The Simultaneous Symbiotic Origin of Mitochondria, Chloroplasts and Microbodies, Annals of the New York Academy of Science, 503, 55-71 Cavalier-Smith, T. (1992) The Number of Symbiotic Origins of Organelles, BioSystems, 28, 91-106 Hartl, F Ostermann, J., Guiard, B and Neupert, W. (1987) Successive Translocation into and out of the Mitochondrial Matrix Targeting of Proteins to the Inner Membrane Space by a Bipartite Signal Peptide, Cell, 51,1027-1037. 

Chloroplasts are enclosed by two membranes. The outer membrane is freely permeable to small molecules (up to about 10 kDa) due to the presence of a porin and the inner membrane is the osmotic barrier and the site where specific transport occurs. The specificity of envelope permeability is strikingly highlighted by the contrast between Pi and PP the former being among the most rapidly translocated molecules and the latter among those to which the envelope is relatively impermeable. Carrier-mediated anion transport can be classified as ... 

Biological membranes show anisotropy, as their molecules are preferentially ordered in a definite direction in the plane of the membrane, and the coupling between chemical reactions (scalar) and diffusion flow (vectorial) can take place. Almost all outer and inner membranes of the cell have the ability to undergo active transport. Sodium and potassium pumps operate in almost all cells, especially nerve cells, while the active transport of calcium takes place in muscle cells. The proton pumps operate in mitochondrial membranes, chloroplasts, and the retina. 

The Tat and YidC systems are also found in certain organelles in eukaryotic cells. The former is present in the thylakoid membrane in plant cells, and the latter is found both in the thylakoid membrane (where it is called the Albino3 system) and in the inner mitochondrial membrane (where it is called the Oxalp system). Both chloroplasts and mitochondria appear to have unique systems for importing proteins across their outer and inner membranes, and these systems also handle membrane proteins. 

Figure 6-6. Proton energy differences across chloroplast lamellar membranes and the mitochondrial inner membrane for various ApH s and AZs s. Data are for 25°C and are calculated using Equation 6.17c.

Figure 6-9. Schematic representation of certain electron flow and ATP synthesis components in the inner mitochondrial membrane, emphasizing the directional flows of H+, various protein complexes, and the ATP synthase. The stoichiometry of H+ per pair of electrons for the protein complexes is tentative. The H+, which is moved toward higher jU,H accompanying electron flow along the respiratory chain, can move back through a hydrophobic channel (F0) and another protein factor attached to the inner membrane (F ), leading to ATP synthesis in the matrix. The lumen side is here designated the Inside, as for chloroplasts (Fig. 6-5).

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