Food Chemistry and Fish in Nutrition

6.4.1.4. Conversion of glucose 6-phosphate into Glycogen

The break down of glycogen to glucose 1-phosphate is carried out by phosphorylase. The synthesis of glycogen involves an entirely different pathway through the formation of uridine diphosphate glucose and the activity of glycogen synthase.

Phosphoglucomutase
Glucose 6-phosphate ↔glucose 1-phosphate

Glucose 1-phosphate uridylyltransferase
Glucose 1-phosphate + UTP →UDP-glucose + PPi

Glycogen synthase
UDP-glucose+ Glycogen Primer (Glucose)n → Glycogen (glucose)n+1

These key enzymes allow reversal of glycolysis to play a major role in gluconeogenesis, the relationships between gluconeogenesis and the glycolytic pathway.

After transamination or deamination, glucogenic amino acids form either pyruvate or members of the citric acid cycle. The reactions described above can account for the conversion of both glucogenic amino acids and lactate to glucose or glycogen. Thus, lactate forms pyruvate and enter the mitochondria before conversion to oxaloacetate and ultimate conversion to glucose.

The source of pyruvate and oxaloacetate for gluconeogenesis is mainly amino acid catabolism. Some amino acids are catabolized to pyruvate, oxaloacetate, or precursors of these. Muscle proteins may break down to supply amino acids. These are transported to liver where they are deaminated and converted to gluconeogenesis inputs.