During gluconeogensis reducing equivalents from mitochondria to cytosol are transported by -

[Medicoman]

During gluconeogensis reducing equivalents from mitochondria to cytosol are transported by -

• 1. Malate
• 2. Aspartate
• 3. Glutamate
• 4. Oxaloacetate

ANS

• Gluconeogenesis is a reversal of glycolytic pathway except for 4 thermodynamic barriers.
• These 4 energy barriers are :-

1. Between pyruvate and phosphoenol pyruvate
2. Between fructose], 6-biphosphate and fructose 6-phosphate
3. Between glucose 6-phosphate and glucose
4. Between glucose 1-phosphate and glycogen

• Reducing equivalents (NADH+H+)are transported from mitochondria to cytosol in overcoming the 1" barrier i.e. ­between pyruvate and phosphoenolpynivate.
• Conversion of pyruvate to phosphoenolpyruvate is achieved by2 enzymes :-

1. Pyruvate carboxylase, a mitochondrial enzyme converts pyruvate to oxaloacetate (OAA).
2. Phosphoenolpyruvate carboxykinase, present chiefly in cytosol, converts OAA to phosphoenolpyruvate.

• It is noted here that OAA is formed inside the mitochondria but the reaction to convert it into phosphoenol pyruvate occurs in cytosol and OAA is not permeable to mitochondrial membrane.
• The OAA is transferred to cytosol by 2 mechanisms :-

1. By formation of Malate
2. By formation of Citrate

• The conversion of OAA to Malate and further of Malate to phosphoenol pyruvate is depicted below. The reducing equivalents (NADH+.1-1+) are transferred across the mitochondrial membrane,along with transport of OAA in the form of malate.