Mitochondrial outer membrane vesicle

As described above, because MAO is bound to mitochondrial outer membranes, MAOIs first increase the concentration of monoamines in the neuronal cytosol, followed by a secondary increase in the vesicle-bound transmitter. The enlarged vesicular pool will increase exocytotic release of transmitter, while an increase in cytoplasmic monoamines will both reduce carrier-mediated removal of transmitter from the synapse (because the favourable concentration gradient is reduced) and could even lead to net export of transmitter by the membrane transporter. That MAOIs increase the concentration of extracellular monoamines has been confirmed using intracranial microdialysis (Ferrer and Artigas 1994). 

Inside the cytoplasm of the presynaptic neuron the monoamines are exposed to the mitochondrial outer membrane-bound enzyme monoamine oxidase (MAO). MAO breaks the monoamines down into inactive metabolites before they are taken up into the vesicles. However, if MAO is inhibited, then the monoamines enter the vesicles and are available for release. MAO inhibitors, such as moclobemide, have been used in the treatment of depression, since they increase the availability of noradrenaline and serotonin. Selegiline is used for Parkinson s disease, since it raises dopamine levels. 

LRRK2 protein is found in the cytosol and mitochondrial outer membrane (West et al., 2005), plasma membrane, lysosomes, endosomes, transport vesicles, Golgi apparatus, a cytoskeleton protein microtubule, synaptic vesicles, and lipid rafts (Biskup et al., 2006 Hatano et al., 2007). Interestingly, a-synuclein is also expressed in the presynaptic membranes and lipid rafts (Fortin et al., 2004). 

Transport of newly synthesized PC from the ER to the mitochondria. Using conventional subcellular fractionation techniques, the transport of nascent PC to the mitochondria of baby hamster kidney cells was examined by pulse-chase experiments with a [ H]choline precursor (M.P. Yaffe, 1983). These experiments show that the newly made PC pool equilibrates between the outer mitochondrial membrane and the ER in approximately 5 min (Fig. 8). Similar studies performed in yeast (G. Daum, 1986) also revealed that the PC pool rapidly equilibrates between the ER and the mitochondria. Addition of metabolic poisons did not eliminate the PC radioequilibration in yeast. Studies with isolated mitochondria demonstrate that PC loaded into the outer mitochondrial membrane can be transported to the inner membrane in an energy-independent manner (M. Lampl, 1994). Consistent with this finding is the observation that PC rapidly moves across the membrane of vesicles derived from mitochondrial outer membranes prepared ifom either mammalian cells or yeast (D. Dolis, 1996 ... 

The most important membranes in animal cells are the plasma membrane, the inner and outer nuclear membranes, the membranes of the endoplasmic reticulum (ER) and the Golgi apparatus, and the inner and outer mitochondrial membranes. Lysosomes, peroxisomes, and various vesicles are also separated from the cytoplasm by membranes. In plants, additional membranes are seen in the plastids and vacuoles. All membranes show polarity—e., there is a difference in the composition of the inner layer (facing toward the cytoplasm) and the outer layer (facing away from it). 

NADH-AFR reductase activity is widely distributed among subcellular membranes such as the outer mitochondrial membrane, endoplasmic reticulum, Golgi apparatus, clathrin-coated vesicles, and the plasma membrane (Sun et aL, 1983). Since NADH-AFR reductase exhibits different properties according to the source membrane, it is likely that activities from different membranes are catalyzed by different enzyme systems (Navas et aL, 1994). 

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