hexose monophosphate pathway pathway

PTS Phosphoenolpyruvate-dependent phosphotransferase system.

TPP = thiamine pyrophosphate.

1 | HMP 2008Dr. Shiva C. Aithal, Dept. of Microbiology, Dnyanopasak College, PARBHANI [email protected]

HEXOSE MONOPHOSPHATE PATHWAY

(HMP pathway or HMP shunt or Oxidative pentose phosphate pathway or Pentose phosphate pathway/cycle or Phosphogluconate pathway or Warburg–Dickens pathway)

A metabolic pathway present in a wide range of prokaryotic and eukaryotic

microorganisms as well as in plants and animals; it involves the oxidative

decarboxylation of glucose 6-phosphate, via 6-phosphogluconate, to ribulose

5-phosphate, followed by a series of reversible, non-oxidative

interconversions whereby hexose and triose phosphates are formed from

pentose phosphates. The generally accepted scheme for the HMP pathway is

shown in figure above. The HMP pathway can serve various functions. The

major one is to provide two molecules of NADPH for each molecule of

glucose which is converted to ribulose 5-phosphate, which in turn is

necessary for biosyntheses of fatty acids. Secondly it provides precursors for

various biosynthetic pathways like

Pentoses for histidine and nucleotide biosynthesis

Erythrose 4-phosphate for aromatic amino acid biosynthesis.

Fructose 6-phosphate may be converted to glucose 6-phosphate and re-

enter the pathway, or may be converted to pyruvate via high-dry

objective reactions of the EMBDEN–MEYERHOF–PARNAS PATHWAY.

Similarly, glyceraldehyde 3-phosphate may be converted to pyruvate via

the latter part of the EMP pathway. In organisms with a functional TCA

CYCLE, pyruvate can be oxidized to yield energy via the TCA cycle and a

respiratory chain. In organisms which lack a complete TCA cycle, pyruvate

may be converted to acetyl-CoA and thence to acetic acid (as in some

acetic acid bacteria). Alternatively, under certain conditions,

glyceraldehyde 3-phosphate can be converted to glucose 6-phosphate (by

reactions of GLUCONEOGENESIS) which can then re-enter the HMP

pathway; in this case, for every six molecules of glucose entering the

pathway, one molecule is effectively completely oxidized. If reducing

equivalents from NADPH can be transferred to NAD+ and thence to an


electron acceptor via a respiratory chain, the pathway can be used to

generate energy even in the absence of a TCA cycle. Other functions of

the HMP pathway include the metabolism of those pentoses which can be

converted to intermediates of the pathway.


hexose monophosphate pathway pathway

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