Ribulose monophosphate route

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The ribulose monophosphate pathway (RuMP), also known as the hexulose phosphate cycle , is used by methanotrophic bacteria to synthesize cell material from formaldehyde (formaldehyde assimilation). This C 1 compound is built up to a triose phosphate in one cycle. The metabolic pathway was found in methanotrophs of type I, whereas methanotrophs of type II assimilate formaldehyde via the serine pathway .

biochemistry

The ribulose monophosphate route to formaldehyde assimilation

In one cycle, three molecules of formaldehyde (CH 2 O) are converted into one molecule of the triose phosphate glyceraldehyde-3-phosphate . Compared to the serine route, the hexulose phosphate cycle is somewhat more efficient. This is because no carbon dioxide is used to build up glyceraldehyde-3-phosphate and no reducing agent , for example in the form of NADH , is required.

In the first step of the assimilation, ribulose-5-phosphate is reacted with formaldehyde to form a hexulose-6-phosphate compound, D- erythro- L- glycero-3-hexulose-6-phosphate. This reaction is catalyzed by a hexulose phosphate synthase. The hexose is then isomerized to fructose-6-phosphate by a hexulose phosphate isomerase. If these steps are carried out three times, the cycle can be completed (see illustration).

Of the three molecules of fructose-6-phosphate, two are built up into fructose-1,6-bisphosphate . This also requires two molecules of ATP . These are split into four molecules of glyceraldehyde-3-phosphate, one of which leaves the cycle. The remaining three molecules with the third molecule of fructose-6-phosphate are converted into three molecules of ribulose by a transaldolase ( EC  2.2.1.2 ), a transketolase ( EC  2.2.1.1 ) and isomerases ( EC  5.3.1.6 ; EC  5.1.3.1 ) 5-phosphate transformed ( pentose phosphate route ). These sugar rearrangements can also be represented as follows:

In sum:

Balance sheet

In total, one molecule of triose phosphate (glyceraldehyde-3-phosphate) is built up from three molecules of formaldehyde:

Individual evidence

  1. ↑ EC  4.1.2.43 hexulose phosphate synthase.
  2. ↑ EC  5.3.1.27 hexulose phosphate isomerase.

literature

  • Georg Fuchs (ed.), Hans. G. Schlegel (Author): General Microbiology . Thieme Verlag Stuttgart, 8th edition 2007, ISBN 3-13-444608-1 , p. 249f.
  • Michael T. Madigan and John M. Martinko: Brock Microbiology . Pearson Studies; 11th updated edition 2009; ISBN 978-3-8273-7358-8 ; P. 658

See also

Web links