Group translocation

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The group translocation is a form of active transport of a substance (usually a monosaccharide , simple sugars such as glucose ) through a cell membrane , wherein energy is consumed and the substance is chemically altered during the transport process.

The substance is phosphorylated during group translocation during the transport process . Since after the conversion, the product inside the cell differs chemically from the substance outside the cell, a concentration gradient along the membrane and thus compensation through back diffusion is avoided. The chemical change in the "cargo" is the point that distinguishes group translocation from other forms of active transport. Group translocation has so far only been found in bacteria .

PEP-PTS in Escherichia coli

Pyruvate

The best studied group translocation system is the so-called phosphotransferase system (PTS) in Escherichia coli , which was discovered and investigated by Saul Roseman in 1964 . In contrast to the usual ATP , phosphoenolpyruvate ( PEP for short ) provides the energy necessary for active transport. In addition to glucose and mannose , the glucosamine N-acetylglucosamine , which is the basic building block of chitin and peptidoglycan, is introduced into the cell by means of group translocation .

Four different proteins are involved in the group translocation transport process:

  • There are three soluble proteins in the cytoplasm : the enzyme I ( EI ), the enzyme IIA ( E IIA ) and the protein HPr
  • a translocator ( E IIB and E IIC ) is fixed in the cell membrane.

Translocation process

Active transport by group translocation through a cell membrane.
  1. First, the phosphate group of the PEP is transferred to the EI ( phosphorylated EI ).
  2. The energy-rich phosphoryl group is transferred from the EI to the protein HPr.
  3. HPr in turn passes the group on to the enzyme E IIA.
  4. E IIA activates the glucose carrier E IIBC, which takes up a monosaccharide such as glucose, transports it through the membrane and phosphorylates it during its passage.

The enzymes IIA, B and C are each specific for the sugar to be transported. So there are different enzymes for all necessary monosaccharides such as glucose, fructose and mannose. Enzyme I and HPr, on the other hand, are involved in every reaction regardless of the type of sugar.

Individual evidence

  1. ↑ Bodo Liedvogel: active transport. In: Lexicon of Biology. Spektrum der Wissenschaft Verlagsgesellschaft, accessed on February 19, 2017 .
  2. ↑ 4: Group Translocators. In: TCDB. Saier Lab Bioinformatics, accessed on September 16, 2010 .
  3. ↑ Heribert Cypionka: Fundamentals of microbiology . 4th, revised and updated edition. Springer, Berlin / Heidelberg 2010, ISBN 978-3-642-05096-1 , p. 137 , doi : 10.1007 / 978-3-642-05096-1 .
  4. ↑ a b Georg Fuchs (Ed.): General Microbiology . 9th, completely revised and exp. Edition. Thieme, Stuttgart 2014, ISBN 978-3-13-444609-8 , p. 340 .