Editing Mitochondrion (section)

===Outer membrane===
The '''outer mitochondrial membrane''', which encloses the entire organelle, is 60 to 75 [[angstrom]]s (Å) thick. It has a protein-to-phospholipid ratio similar to that of the [[cell membrane]] (about 1:1 by weight). It contains large numbers of [[integral membrane protein]]s called [[porin (protein)|porins]]. A major trafficking protein is the pore-forming [[voltage-dependent anion channel]] (VDAC). The [[Voltage-dependent anion channel#Biological function|VDAC]] is the primary transporter of [[nucleotide]]s, [[ion]]s and [[metabolite]]s between the [[cytosol]] and the intermembrane space.<ref name="Blachly-Dyson-2001">{{cite journal | vauthors = Blachly-Dyson E, Forte M | title = VDAC channels | journal = IUBMB Life | volume = 52 | issue = 3–5 | pages = 113–118 | date = September 2001 | pmid = 11798022 | doi = 10.1080/15216540152845902 | doi-access = free }}</ref><ref name="Hoogenboom-2007">{{cite journal | vauthors = Hoogenboom BW, Suda K, Engel A, Fotiadis D | title = The supramolecular assemblies of voltage-dependent anion channels in the native membrane | journal = Journal of Molecular Biology | volume = 370 | issue = 2 | pages = 246–255 | date = July 2007 | pmid = 17524423 | doi = 10.1016/j.jmb.2007.04.073 }}</ref> It is formed as a [[beta barrel]] that spans the outer membrane, similar to that in the [[gram-negative]] [[bacterial outer membrane]].<ref name="Zeth-2010">{{cite journal | vauthors = Zeth K | title = Structure and evolution of mitochondrial outer membrane proteins of beta-barrel topology | journal = Biochimica et Biophysica Acta (BBA) - Bioenergetics | volume = 1797 | issue = 6–7 | pages = 1292–1299 | date = June 2010 | pmid = 20450883 | doi = 10.1016/j.bbabio.2010.04.019 | doi-access = free }}</ref> Larger proteins can enter the mitochondrion if a signaling sequence at their [[N-terminus]] binds to a large multisubunit [[Mitochondrial membrane transport protein|protein]] called [[Translocase of the outer membrane|translocase in the outer membrane]], which then [[active transport|actively moves]] them across the membrane.<ref name="Herrmann-2000">{{cite journal | vauthors = Herrmann JM, Neupert W | title = Protein transport into mitochondria | journal = Current Opinion in Microbiology | volume = 3 | issue = 2 | pages = 210–214 | date = April 2000 | pmid = 10744987 | doi = 10.1016/S1369-5274(00)00077-1 | url = http://nbn-resolving.de/urn:nbn:de:bvb:19-epub-7488-5 }}</ref> Mitochondrial [[protein precursor|pro-proteins]] are imported through specialised translocation complexes.

The outer membrane also contains [[enzyme]]s involved in such diverse activities as the elongation of [[fatty acid]]s, [[oxidation]] of [[epinephrine]], and the [[Biodegradation|degradation]] of [[tryptophan]]. These enzymes include [[monoamine oxidase]], [[rotenone]]-insensitive NADH-cytochrome c-reductase, [[kynurenine]] [[hydroxylase]] and fatty acid Co-A [[ligase]]. Disruption of the outer membrane permits proteins in the intermembrane space to leak into the cytosol, leading to cell death.<ref name="Chipuk-2006">{{cite journal | vauthors = Chipuk JE, Bouchier-Hayes L, Green DR | title = Mitochondrial outer membrane permeabilization during apoptosis: the innocent bystander scenario | journal = Cell Death and Differentiation | volume = 13 | issue = 8 | pages = 1396–1402 | date = August 2006 | pmid = 16710362 | doi = 10.1038/sj.cdd.4401963 | doi-access = free }}</ref> The outer mitochondrial membrane can associate with the endoplasmic reticulum (ER) membrane, in a structure called MAM (mitochondria-associated ER-membrane). This is important in the ER-mitochondria calcium signaling and is involved in the transfer of lipids between the ER and mitochondria.<ref name="Hayashi-2009"/> Outside the outer membrane are small (diameter: 60 Å) particles named sub-units of Parson.