Stickland reaction

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General presentation of the paired fermentation of amino acids. The reduction equivalents are shown in simplified form with 2 [H], n = 1.2. For example, if alanine and two molecules of glycine are fermented, R 1 = CH 3 , R 2 = H and n = 2.

A Stickland reaction is the coupled fermentation of two different amino acids with simultaneous deamination , whereby one amino acid is oxidized and the other amino acid is reduced . This type of fermentation serves as an energy source for some organisms. The Stickland reaction is a specialty in the fermentation of amino acids . The metabolic pathway owes its name to its discoverer, Leonard Hubert Stickland .

Occurrence

Organisms that gain energy through stickland reactions are typically representatives of amino acid-utilizing clostridia in the broader sense - a polyphyletic group of anaerobic bacteria within the Firmicutes . Typical representatives are, for example, Clostridium sticklandii , C. sporogenes and C. botulinum . However, since only a tiny fraction of all bacteria and archaea have been described and classified by isolates to date , it is of course not clear whether Stickland reactions are limited to only a few phylogenetic groups.

biochemistry

Example of a Stickland reaction in which one molecule of D -alanine and two molecules of glycine are fermented to acetate. Please see text for details.

Stickland was the first to recognize that there are bacteria that only ferment combinations of two amino acids, but do not use these amino acids individually. He found that C. sporogenes (NCTC 533) made significant use of six different combinations. Hence the umbrella term Stickland reaction for this type of reaction.

There are two branches in each of the Stickland reactions:

In the oxidative branch , the amino acid is deaminated to form an α-keto acid . This is then oxidatively decarboxylated with the incorporation of coenzyme A to form an “activated” fatty acid (acyl-CoA) . The high-energy thioester bond of the acyl-CoA is obtained by means of inorganic phosphate to form acyl phosphate. The phosphate residue of the acyl phosphate is finally transferred to adenosine diphosphate (ADP) with the formation of adenosine triphosphate (ATP). This substrate chain phosphorylation generates energy in the oxidative branch. The original carbon chain of the amino acid is one carbon atom shorter after fermentation.

As a result of the reductive deamination of the second amino acid in the reductive branch , the hydrogen or electron carriers formed are oxidized and thus regenerated. A fatty acid is created from the amino acid , whereby the number of carbon atoms is retained.

A typical Stickland reaction is shown in the figure using the example of C. sporogenes , which simultaneously oxidizes D - alanine and reduces two molecules of glycine . An aminotransferase deaminates alanine to pyruvate and α-ketoglutarate is aminated to L - glutamate . The glutamate is then reoxidized to α-ketoglutarate by an NAD + -dependent dehydrogenase, releasing NH 4 + ( ammonium ). Some clostridia can also oxidize alanine directly to pyruvate by an NAD + -dependent alanine dehydrogenase .

The resulting pyruvate is oxidatively decarboxylated by a pyruvate ferredoxin oxidoreductase using coenzyme A in acetyl-CoA . This reduces ferredoxin. Acetyl-CoA is transesterified to acetyl phosphate by a phosphotransacetylase . This is converted into acetate in the course of the substrate chain phosphorylation , in this step ATP is produced. The enzyme involved in the reaction is an acetate kinase.

In the reductive branch, two molecules of glycine are converted into two molecules of acetyl phosphate by a glycine reductase containing selenium or selenocysteine . As in the oxidative branch, acetate is then produced from these, whereby additional energy can be obtained.

Substrate diversity

In addition to alanine, methionine , leucine , isoleucine , valine , serine , threonine and histidine can serve both as electron acceptors and as electron donors. In the reductive branch, in addition to glycine, arginine , leucine, tryptophan , phenylalanine , tyrosine , hydroxyproline and proline also function as electron acceptors .

Non -proteinogenic amino acids , such as D- proline, can also be used, so that an enormous number of stickland reactions is conceivable, used by different specialists. However, only in the case of glycine can ATP also be formed in the reductive branch via acetyl phosphate. Proline is not deaminated, but reduced to δ-aminovalerate through ring cleavage .

Individual evidence

  1. ^ Nisman, B. (1954): The Stickland Reaction . In: Bacteriol Rev 18 (1): 16-42. PMID 13140081 ; PMC 180783 (free full text, PDF).
  2. a b Stickland, LH. (1934): Studies in the metabolism of the strict anaerobes (genus Clostridium ): The chemical reactions by which Cl. sporogenes obtains its energy . In: Biochem J . 28 (5); 1746-1759. PMID 16745572 ; PMC 1253397 (free full text, PDF).
  3. ^ Nigel P. Minton (eds.) And David J. Clarke (eds.): Clostridia ; Springer-Verlag; 2nd edition 1989; ISBN 0-306-43261-7 ; P. 46.
  4. a b Andreesen, JR. (1994): Glycine metabolism in anaerobes. In: Antonie Van Leeuwenhoek . 66 (1-3); 223-237; PMID 7747933 ; doi : 10.1007 / BF00871641 .
  5. Georg Fuchs (Ed.), Hans. G. Schlegel (Author): General Microbiology . 8th edition, Thieme Verlag, Stuttgart 2007; ISBN 3-13-444608-1 ; P. 374.
  6. Michael T. Madigan, John M. Martinko, Jack Parker and Thomas D. Brock: Microbiology . Spektrum Akademischer Verlag, Heidelberg et al. O. 2002, ISBN 3-8274-0566-1 , p. 568.
  7. Stickland, LH. (1935): Studies in the metabolism of the strict anaerobes (Genus Clostridium): The reduction of proline by Cl. sporogenic . In: Biochem J. Vol. 29, No. 2, pp. 288-290, PMID 16745669 ; PMC 1266487 (free full text, PDF).

literature

  • Georg Fuchs (ed.), Hans. G. Schlegel (Author): General Microbiology . 8th edition, Thieme Verlag, Stuttgart 2007, ISBN 3-13-444608-1 , p. 374.
  • Katharina Munk (Ed.): Pocket textbook Biology: Microbiology . Thieme Verlag, Stuttgart 2008; ISBN 978-3-13-144861-3 ; Pp. 385-386.
  • Michael T. Madigan, John M. Martinko, Jack Parker, and Thomas D. Brock: Microbiology . Spektrum Akademischer Verlag, Heidelberg et al. O. 2002, ISBN 3-8274-0566-1 , pp. 567-568.
  • Wolfgang Fritsche: Microbiology . 3. rework. Edition, Spektrum Akademischer Verlag, Heidelberg 2002; ISBN 3-8274-1107-6 , pp. 250-251.

See also