Envelope membrane inner

Plant cells contain a unique family of organelles, the plastids, of which the chloroplast is the prominent example. Chloroplasts have a double membrane envelope, an inner volume called the stroma, and an internal membrane system rich in thylakoid membranes, which enclose a third compartment, the thylakoid lumen. Chloroplasts are significantly larger than mitochondria. Other plastids are found in specialized structures such as fruits, flower petals, and roots and have specialized roles. 

The nuclear envelope is composed of the nuclear membranes (inner and outer), the nuclear lamina, and the nuclear pore complexes. The inner and outer nuclear membranes are connected at the nuclear pore sites and enclose a flattened sac... 

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. 

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. 

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. 

The structure, ultrastructure and formation of the hymenolepidid egg has been reviewed in detail by Ubelaker (888). Its general morphology is shown in Fig. 7.14). Although there are only the usual three basic embryonic membranes (p. 179) in the developing egg - shell/capsule, outer envelope, and inner envelope - the fully formed egg often appears to be more complex due to further differentiation of these layers. The following structures can be recognised (Fig. 7.11). 

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). 

PEND protein DNA-binding protein in the inner envelope membrane of the developing chloroplast... 

The carrier protein facilitating Pj and phosphate ester transport is of particular interest in leaves in connection with carbon processing - i.e., the synthesis, transport and degradation of carbohydrate, all of which occur in the cytosol [51]. This metabolite carrier, called the phosphate translocator, is a polypeptide with a molecular mass of 29 kDa and is a major component of the inner envelope membrane [52,53]. The phosphate translocator mediates the counter-transport of 3-PGA, DHAP and Pj. The rate of Pj transport alone is three orders of magnitude lower than with simultaneous DHAP or 3-PGA counter-transport [54]. Consequently operation of the phosphate translocator keeps the total amount of esterified phosphate and Pj constant inside the chloroplast. Significantly, the carrier is specific for the divalent anion of phosphate. 

To prevent overheating, the covering could be ventilated naturally by using the physical effects of the Bernoulli flow and also by means of an air-conditioning system within the envelope. The inner membrane was... 

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). 

A specific transport of malate and oxaloacetate across the inner envelope membrane enables a transfer of redox equivalents from the chloroplast stroma to the cytosol (8). The translocator involved is half saturated at very low concentrations of oxaloacetate (Km 9 pM). OAA transport is insensitive to even high concentrations of malate (Ki 1.4 mM) as determined in spinach chloroplasts. The large redox gradient between the NADPH/NADP in the stroma and the NADH/NAD in the cytosol. 

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

Flg. 13. The chloroplast envelope plays a predominant role in the assembly of the three parts of the galactolipid molecule (galactose, glycerol, fatty acids). Saturated and monounsat-urated fatty acids are synthesized in the stroma by a multienzyme complex (fatty acid synthetase). Then, the different steps occur on the envelope, probably at the level of the inner membrane. Under these conditions, massive transport of galactolipids should occur very rapidly between the inner layer of the inner envelope membrane and the thylakoids (reproduced from Douce and Joyaid, 1979a, by permission). 

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). 

Shingles, R. North, M. McCarty, R. E. Ferrous ion transport across chloroplast inner envelope membranes. Plant Physiol. 2002, 128, 1022-1030. 

Pig 3 Synthesis of n-tocopherol /5,6,12/ from homogentlsate /10/ and phytyl-pp at the inner envelope membrane of chloroplasts/8/. Plastoqulnone-9 (see text and Fig. 4) is synthesized from homogentlsate and nonaprenyl-(solanesyl-)pp at the same membrane /6,8/. For synthesis of homogentlsate /II/ and phytyl-PP / / in chloroplasts see text. 

The reaction mechanism of PQ synthesis equals that of aT synthesis. The synthesis also occurs exclusively at the inner chloroplast envelope membrane /8/ (Fig. 4), however, it can be assumed that either prenylquinone is formed by its own enzyme garniture. 2-Methyl-6-nonaprenyl-(solanosyl-)qulnol is formed from homogentlsate plus nonaprenyl-(solanosyl-)PP. The quinol formed is then methylated by SAM to yield PQH /6/ (Fig. 4). Even if the sequence in PQ synthesis is clarified Homogentlsate — 2-Methyl-6—nonaprenylqulnol —PQH. no data are available for the synthesis of hydroxylated quinones... 

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