Biochemistry of Fruits - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 29

Starch

β -Amylase

α -Amylase

Starch phosphorylase

Maltose

Glucose

α -Glucosidase

Glucose-1-phosphate

Glucose phosphate mutase

Glucose-6-phosphate

Glycolysis

Glyceraldehyde-3-phosphate

Chloroplast

Cytoplasm

Fructose-1,6,-diphosphate

Fructose bisphosphatase Phosphfructophosphotransferase

Fructose-6-phosphate

Glucose-6-phosphate

Glucose-1-phosphate

Sucrose
phosphorylase

UTP

Uridine diphosphate glucose

Glucose

Sucrose-6-phosphate

Sucrose

Sucrose phosphatase

Invertase Fructose

Starch-sugar interconversions in plants and metabolite transfer from chloroplast to the cytoplasm.

Fig. 3.2

pyrophosphorylase in the presence of UTP (uridine triphosphate). UDP-glucose is also an
important substrate for the biosynthesis of cell wall components such as cellulose. UDP-
glucose is converted to sucrose-6-phosphate by the enzyme sucrose phosphate synthase,
which utilizes fructose-6-phosphate during this reaction. Finally, sucrose is formed from
sucrose-6-phosphate by the action of phosphatase with the liberation of the inorganic phos-
phate.
Even though sucrose biosynthesis is an integral part of starch metabolism, sucrose often
is not the predominant sugar that accumulates in fruits. Sucrose is further converted into
glucose and fructose by the action of invertase, which is characteristic to many ripe fruits.