module: dmel_polyol_pathway
title: Polyol pathway in Drosophila melanogaster
label: Polyol pathway
module_type: METABOLIC_PATHWAY
description: >-
  The polyol pathway converts glucose to fructose in two steps. An NADPH-dependent
  aldose reductase of the aldo-keto reductase 1B family reduces glucose to
  sorbitol, and an NAD+-dependent sorbitol dehydrogenase oxidises sorbitol to
  fructose. Drosophila has two aldose reductase genes in the FlyBase group (Ar1
  and Ar2) and two sorbitol dehydrogenase genes (Sord1 and Sord2).
summary: >-
  Two-step conversion of glucose to fructose through sorbitol by aldose
  reductase and sorbitol dehydrogenase.
concepts:
  - {id: GO:0046370, label: fructose biosynthetic process}
parts:
  - id: aldose_reduction
    label: Aldose reduction
    role: step 1, glucose to sorbitol
    module_type: REACTION
    genes: [Ar1, Ar2]
    function: {id: GO:0004032, label: aldose reductase (NADPH) activity}
    unit_functions:
      Ar2: null
  - id: sorbitol_oxidation
    label: Sorbitol oxidation
    role: step 2, sorbitol to fructose
    module_type: REACTION
    genes: [Sord1, Sord2]
    function: {id: GO:0003939, label: "L-iditol 2-dehydrogenase (NAD+) activity"}
connections:
  - source: aldose_reduction
    target: sorbitol_oxidation
    connection_type: PRECEDES
    description: Sorbitol made by aldose reductase is oxidised to fructose.
notes: >-
  Ar1 and Ar2 are alternative aldose reductases and Sord1 and Sord2 alternative
  sorbitol dehydrogenases; each gene is a separate annoton. The aldose reductase
  activity is given to Ar1, which has been assayed; Ar2 is assigned to the step
  by FlyBase and sequence similarity only, so no molecular function is given.
  Ar1 belongs to a family of broad-specificity aldo-keto reductases that also
  reduce other aldehydes, so its physiological substrates are not limited to
  glucose.