Cytosolic space

Conventional electron microscopy (Devine et al 1972) and freeze-etch (Somlyo Franzini-Armstrong 1985) of VSMCs reveals that the jSR is separated from overlying PL by a 12—15nm cytosolic space that is traversed by electron-dense structures. These structures appear similar to the foot processes of cardiac and skeletal muscle (Franzini-Armstrong et al 1998). Indeed, there is striking structural similarity between these PL—jSR regions in VSMC and the diads and triads of cardiac and skeletal muscle (Franzini-Armstrong et al 1998). Moreover,... 

In this chapter, we describe a molecular interaction between cytochrome c and cardiolipin which prevents peroxidation of the lipid, implying that cardiolipin may play an important role in determination of the fate of the cell. In other words, a peroxidation of cardiolipin may well allow cytochrome c to discharge from the mitochondrial inner membrane into the cytosolic space during apoptotic cell death. 

Figure 8.6. Oxidative phosphorylation of the mitochondria, showing the four complexes of the electron transport chain that pump protons across the inner mitochondrial membrane into the cytoplasmic side to produce a higher concentration of proton within the inner membrane cytosolic space and showing the ATP synthase (at right) that uses the proton flow,...

Complex I Oxidizes one molecule of NADH, and, by an as yet unknown mechanism, pumps 4 protons into the intermembrane (cytosolic) space and reduces ubiquininone (coenzyme Q) to produce ubiquinol, QH2. Overall equation ... 

The space inside the inner mitochondrial membrane is called the matrix, and it contains most of the enzymes of the TCA cycle and fatty acid oxidation. (An important exception, succinate dehydrogenase of the TCA cycle, is located in the inner membrane itself.) In addition, mitochondria contain circular DNA molecules, along with ribosomes and the enzymes required to synthesize proteins coded within the mitochondrial genome. Although some of the mitochondrial proteins are made this way, most are encoded by nuclear DNA and synthesized by cytosolic ribosomes. 

Cytochrome c, like UQ is a mobile electron carrier. It associates loosely with the inner mitochondrial membrane (in the intermembrane space on the cytosolic side of the inner membrane) to acquire electrons from the Fe-S-cyt C aggregate of Complex 111, and then it migrates along the membrane surface in the reduced state, carrying electrons to cytochrome c oxidase, the fourth complex of the electron transport chain. 

Most of the NADH used in electron transport is produced in the mitochondrial matrix space, an appropriate site because NADH is oxidized by Complex I on the matrix side of the inner membrane. Furthermore, the inner mitochondrial membrane is impermeable to NADH. Recall, however, that NADH is produced in glycolysis by glyceraldehyde-3-P dehydrogenase in the cytosol. If this NADH were not oxidized to regenerate NAD, the glycolytic pathway would cease to function due to NAD limitation. Eukaryotic cells have a number of shuttle systems that harvest the electrons of cytosolic NADH for delivery to mitochondria without actually transporting NADH across the inner membrane (Figures 21.33 and 21.34). 

At the level of a single channel, addition of ACh is followed by transient openings of the channel. The current i flowing through an open channel is 4 pA at a membrane potential Voi-l 00 mV. Since one ampere (A) represents the flow of 6.24-1018 charges per second, 2.5-107 Na+ ions per second flow through an open channel. The conductance g of a plasma membrane channel is the measure of the ease of flow of cuirent between the extracellular space and the cytosol or vice... 

The mitochondrion has an outer and an inner membrane (Figure 1). The outer membrane contains pores formed from a protein, porin, which allow exchange of molecules with molecular weights up to about 2,000 between the cytosol and the intermembrane space. The inner membrane is extensively invaginated to increase its surface area. It has a different lipid composition from the outer membrane and is rich in the acidic phospholipid cardiolipin (diphosphatidyl-glycerol) which is only found in animal cells in mitochondria. Cardiolipin confers good electrical insulating properties on the inner membrane which is impermeable... 

Exactly how this transporter carries noradrenaline across the neuronal membrane is not known but one popular model proposes that it can exist in two interchangeable states. Binding of Na+ and noradrenaline to a domain on its extracellular surface could trigger a conformation change that results in the sequential opening of outer and inner channel gates on the transporter. This process enables the translocation of noradrenaline from the extracellular space towards the neuronal cytosol. 

Adenylate kinase (AK) is a ubiquitous monomeric enzyme that catalyzes the interconversion of AMP, ADP, and ATP. This interconversion of the adenine nucleotides seems to be of particular importance in regulating the equilibrium of adenine nucleotides in tissues, especially in red blood cells. AK has three isozymes (AK 1,2, and 3). AK 1 is present in the cytosol of skeletal muscle, brain, and red blood cells, and AK 2 is found in the intermembrane space of mitochondria of liver, kidney, spleen, and heart. AK 3, also called GTP AMP phosphotransferase, exists in the mitochondrial matrix of liver and heart. 

Transcriptional inhibitors could be used simultaneously. Rifampicin blocks chloroplast and mitocondrian RNA synthesis [23, 24], while tagetitoxin is a very specific inhibitor of chloroplast RNA polymerase [25]. Treatment with these antibiotics does not inhibit Rubisco SSU synthesis since the promoter is part of the nuclear genome, while the cytosolic ribosomes are not affected by streptomycin. Therefore SSU promoters can be used to drive transgene expression and facilitate the accumulation of recombinant proteins. Expressed proteins are targeted to a suitable cellular compartment, such as the cytoplasm, apoplastic space or chloroplast, depending on the nature of the protein. 

Adenosine is not a classical neurotransmitter because it is not stored in neuronal synaptic granules or released in quanta. It is generally thought of as a neuromodulator that gains access to the extracellular space in part from the breakdown of extracellular adenine nucleotides and in part by translocation from the cytoplasm of cells by nucleoside transport proteins, particularly in stressed or ischemic tissues (Fig. 17-2C). Extracellular adenosine is rapidly removed in part by reuptake into cells and conversion to AMP by adenosine kinase and in part by degradation to inosine by adenosine deaminases. Adenosine deaminase is mainly cytosolic but it also occurs as a cell surface ectoenzyme. 

The enzyme superoxide dismutase (SOD) occurs in three forms in mammalian systems (1) CuZnSOD (SOD1) found in the cytosol, (2) MnSOD (SOD2) found in mitochondria, and (3) CuZnSOD found in extracellular space (SOD3). Additionally, many bacterial SOD enzymes contain iron. SOD 1 has been discussed in detail... 

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