Envelope membrane outer

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. 

Most chloroplastic proteins, except those of the outer envelope membrane, have an N-terminal extension that is usually cleaved during matu-... 

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. 

Part of the sorting pathway to the outer envelope membrane (such as Toc75) is mediated by a bipartite signal that consists of the chloroplast... 

The inner envelope membrane proteins have a cleavable N-terminal transit peptide, as well as some hydrophobic domain (s) in their mature portion. There are two possibilities on the role of this hydrophobic domain it may work as an N-terminal signal peptide after the translocation into the stroma and the subsequent cleavage of the transit peptide. Alternatively, it may work as a stop-transfer signal. One more important question is how the distinction is made between the outer membrane proteins, the inner membrane proteins, and the thylakoid membrane proteins. It is still an enigma. 

Li, H.-M., and Chen, L.-J. (1996). Protein targeting and integration signal for the chloro-plastic outer envelope membrane. Plant Cell 8, 2117-2126. 

There is no clear evidence for this type of localization, since most eukaryotic P450s are anchored on the cytoplasmic face of the endoplasmic reticulum (ER) membrane by a hydrophobic domain in their N-terminus. The association of some cytochrome P450s with the inner mitochondrial membrane in animals,17 and with the outer envelope membranes of chloroplasts18 shows that different plant organelles... 

Chloroplasts in higher plants have three membranes the outer and inner envelope membranes and the thylakoid membrane. Very little is known about membrane protein assembly into the two envelope membranes (Soil and Tien, 1998). The thylakoid has been better studied and in fact appears to use mechanisms very similar to those found in E. coli for membrane protein insertion (Dalbey and Robinson, 1999). Thus, SRP, SecA, SecYEG, YidC, and Tat homologues are all present in the thylakoid membrane or in the stroma (the Tat system was first identified in thylakoids, in fact). In contrast to E. coli, however, there are thylakoid proteins that appear to insert spontaneously into the membrane, insofar as no requirement for any of the known translocation machineries has been detected (Mant et al, 2001). 

Transcripts of cab genes are translated on cytoplasmic polysomes to produce soluble precursor forms of the polypeptides approximately 3-4 kDa larger than the mature form [76]. The precursors bind to the outer envelope membrane of the chloroplasts [77] before being imported into the chloroplasts by an energy-de-pendent process [78]. The mechanism by which the soluble precursors cross the two envelope membranes is not known, but translocation may occur in regions where the two envelope membranes are appressed. After uptake, the transit pep-... 

The nucleus is a large membrane-bound cell organelle which houses the chromosomes and which occupies roughly 10% of the volume of all eukaryotic cells. The nucleus is separated from the rest of the cell and the cytoplasm by a double membraue known as the nuclear envelope. The outer layer of the nuclear membrane is studded with small openings called nuclear pores, which allow for the controlled movement of selected molecules in and out of the nucleus. Most of a eukaryotic cell s DNA is found in the chromosomes of the nucleus, while a very small amount of DNA is present in the mitochondria. All plant and animal cells with a nucleus and known as eukaryotic cells, (meaning true nucleus) while bacterial cells which lack a nucleus are known as prokaryotic cells. 

SEPARATION OF STROMAL, THYLAKOID, INNER AND OUTER ENVELOPE MEMBRANE PROTEINS OF SPINACH CHLOROPLASTS INTO HYDROPHILIC AND HYDROPHOBIC FRACTIONS... 

After isolation of intact spinach chloroplasts, four fractions were obtained mostly according to (6) thylakoid, inner and outer envelope membranes and stroma. The polypetides belonging to the envelope lumen should now be found in the stroma and/or the inner and outer envelope membranes, depending on the interactions involved. These four fractions were submitted to TX-114 phase partition and then separated by SDS-PAGE (fig.1). As expected, all but four of the stroma polypeptides partitioned in the aqueous phase and the recovery was excellent. The recovery was also quite good in the membranes when strongly hydrophobic or hydrophilic polypeptides were concerned the thylakoid 32 and 23 kDa, the inner membrane 34 kDa were exclusively recovered in the organic phases, while the outer membrane 109, 40, 16 and 14 kDa... 

Case 3 Stroma, Inner and Outer envelope membranes 54 kPa After proteosynthesis and TX-114 phase partition, a radioactive 54 kDa band was found in the organic phases of the stroma, the inner and outer envelope membranes at the level of the RubisCO large subunit (LS) (fig.1). The RubisCO is a known contaminant of the envelope membrane and has been, so far, impossible to eliminate. As the TX-114 partitioning was shown to be reliable, we tried to find out whether this 54 kDa Coomassie band was the LS or not. First, an antibody against the RubisCO (kindly provided by Dr. A. Radunz) was tested on the three treated fractions as well as on their respective controls (fig.2). 

Separation of Stromal, Thylakoid, Inner and Outer Envelope Membrane Proteins of Spinach Chloroplasts into Hydrophilic and Hydrophobic Fractions 849... 

Neuhaus, H.E. Wagner, R. (2000). Solute pores, ion channels, and metabohte transporters in the outer and iimer envelope membranes of higher plant plastids. Biochimica et Biophysica Acta -Biomembranes, 1465, 307 323. 

Chloroplasts were isolated and purified as described previously (2) from destarched 11-12 day old pea seedlings (16 h photoperiod 21C day 16i night). Inner (lEM) and outer (OEfI) envelope membranes were isolated as described by Nguyen et al (3). 

There is a similar situation in all the membranes in contact with the cytosol PC is a major constituent in the outer membrane from plastids and mitochondria and in the peroxisomal membrane (table l). One can question whether this situation has any physiological significance or results from the functionning of the phospholipid transfer proteins that are present in the cytosol. There is almost no redistribution of this PC whithin the chloroplast since phospholipase C treatment destroy almost all the envelope PC without rupture or modification of the outer envelope membrane structure. ... 

UDPgal transferase (UDPGT) activity has been localized in the outer chloroplast envelope membrane (OEM) of pea (18 3 plant) (1) and in the inner chloroplast envelope membrane (lEM) of spinach (16 3 plant) (2). 

The cyanobacteria (blue-green algae) are classified as Gram-negative bacteria (Stanier et al., 1976). Their cell envelope is composed of the outer membrane and plasma (or cytoplasmic) membrane separated by a peptido-glycan layer. In addition, they have intracellular photosynthetic membranes, i.e., the thylakoid membranes. Their membrane structure is similar to that of eukaryotic plant chloroplast, which contains outer and inner envelope membranes, surrounding the thylakoid membranes. 

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