Oxidative phosphorylation

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The oxidative phosphorylation is a biological process in all aerobic takes place beings. It is part of the energy metabolism and is used to generate energy in the form of ATP . The energy required to produce ATP is obtained by means of the respiratory chain and converted into chemical energy with the help of chemiosmotic coupling . Transport proteins are also involved .

Enzymes involved

Respiratory chain

Complex V

F o F 1 -ATP synthase . Complex V, which finally synthesizes ATP, consists of two parts: the F 1 part protrudes into the mitochondrial matrix, while the F o part forms a proton channel through the inner mitochondrial membrane. With the aid of the above-switched four complexes of the respiratory chain was proton gradient and thus an electro-chemical potential .DELTA.P constructed by H + ions to the outside in the intermembrane space pumped are, against the positive there voltage ΔΨ and the higher there proton concentration ApH. This creates the driving force of the protons towards the matrix of the mitochondrion. The F o subunitrepresents the appropriate channel. Comparable to a turbine - and a rotation of the F o part could actually be detected - the proton flow releases energy that is used for the synthesis of ATP by the F 1 subunit. (see mechanism of ATP synthase )

The question of how many protons are required for the synthesis of an ATP molecule from ADP and inorganic phosphate is still a matter of dispute . According to Löffler, Petrides: at least 3 , whereby another proton ( i.e. at least 4 in total ) appears in the balance that was required for the transport of phosphate (through phosphate / H + symport) into the matrix space.

Depending on how many c subunits the transmembrane ring (F o c ring) consists of, a different number of protons must be transported through F o into the matrix. There can be 10-14 subunits. F 1 forms 1 molecule of ATP for every 120 ° rotation of the gamma unit - i.e. 3 molecules of ATP for a complete rotation (360 °). 4 protons are required for the formation of an ATP molecule by the ATP synthase from E. coli or chloroplasts .

Transport proteins

ATP / ADP translocase

ATP-ADP translocase and phosphate transporter

The ATP produced by complex V cannot freely pass through the inner mitochondrial membrane. Conversely, the ADP required for ATP synthase cannot diffuse from the cytosol into the matrix. However, there is a special transport system to bring ATP into the cytosol and ADP into the matrix, the so-called ATP / ADP translocase (see there).

The translocase is a common protein to the inner membrane of the mitochondrion and may constitute up to 14% of all proteins of the inner membrane. As a result, ATP synthesis is unlikely to be limited due to a lack of ADP.

Phosphate transporter

Phosphate is also required for the synthesis of ATP from ADP. Neither can ATP or ADP diffuse through the inner membrane of the mitochondrion. The transport is made possible by a special symporter , the mitochondrial phosphate transporter , which simultaneously transports a proton and a phosphate molecule from the intermembrane space into the matrix. Its activity can be inhibited by Mersalyl .

Individual evidence

  1. ^ Georg Löffler, Petro E. Petrides: Biochemistry and Pathobiochemistry . Springer-Verlag, Berlin; 8th edition 2007; ISBN 978-3-540-32680-9 ; Wikibooks .
  2. Stefan Steigmiller, Paola Turina, Peter Gräber: The thermodynamic H + / ATP ratios of the H + -ATPsynthases from chloroplasts and Escherichia coli . In: Proceedings of the National Academy of Sciences . 105, No. 10, 2008, pp. 3745-3750.
  3. Thomas M. Devlin (Ed.): Textbook of Biochemistry with Clinical Correlations . Wiley & Sons; 6th edition 2005; ISBN 0-471-67808-2 ; P. 570.