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Pathway details: proline degradation

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  Pathway was created on Mon Jul 29, 2013.
 Contributed by aracyc:
Supporting evidence for this pathway in Arabidopsis: This pathway is on the list of Ubiquitous Plant Pathways, which includes pathways that are thought to be present in all or most land plants. [more info] Summary from MetaCyc: L-proline can be catabolized to L-glutamate by the action of two enzymatic activities: proline dehydrogenase (PDH) (sometimes referred to as proline oxidase) and Δ-pyrroline-5-carboxylate dehydrogenase (P5CDH). Whereas in eukaryotes PDH and P5CDH are encoded by two different genes, in most bacteria, including enteric bacteria , , , , , and , both steps are catalyzed by a single polypeptide encoded by the putA gene. The enzyme is highly conserved among different microorganisms, but its genetic organization and control of expression are highly divergent . Saccharomyces cerevisiae is able to utilize proline as a sole nitrogen source. L-proline is catabolized within the mitochondrial matrix. Since both enzymes are encoded in the nucleus and synthesized in the cytoplasm, they are imported into the mitochondria before they become active . L-proline can serve as a total source of carbon and energy or of nitrogen for Escherichia coli. In the two steps (both of which are catalyzed by a product of putA) shown here, proline is converted to L-glutamate, which is further degraded to α-ketoglutarate, an intermediate of the . Curiously, L-glutamate, the obligate intermediate of the L-proline degradation pathway, cannot itself serve as a total source of carbon and energy for E. coli because L-glutamate transport supplies exogenous L-glutamate at an inadequate rate. Sometimes the L-proline degradation pathway is shown in three steps because L-glutamate γ-semialdehyde is an intermediate between pyrroline 5-carboxylate and L-glutamate. The conversion of pyrroline 5-carboxylate to L-glutamate occurs spontaneously although the putA product might stimulate the reaction. In addition to its being a building block of proteins, L-proline acts as an osmotic protectant. Consistent with this latter role, high osmolarity inhibits L-proline degradation. Reviewed in Reitzer, L., EcoSal Module 3.4.7 |CITS: [ecosal]|
  Parts of this pathway occur in:   cytosol     mitochondrion     nucleus  

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