Fructose metabolism

Metabolism of fructose in muscle and extra hepatic tissue

Fructose

Fructose -6-phosphate

Glucose 6 Phosphate

ATP

ADP

Hexokinase

Pyruvate Glycolysis

Glycogen

F1,6 BP

Phosphohexose isomerase

Metabolism of fructose in Liver

Fructose

Fructose -1- phosphate

Glyceraldehyde

ATP

ADP

Fructokinase

TAG Glycero phospholipid

Aldolase B

DHAP

Glycerol 3 P

Alcohol DH Glycerol

NAD NAD H + H

Glycero kinase

ATP

ADP

Glycolysis Gluconeogenesis

1

2

34

5

6

Formation of Sorbitol

D-Glucose

NADPH+H+

NADP+

ALDOSEREDUCTASE

(not found in liver)D-Sorbitol

SORBITOLDEHYDROGENASE

NAD+

NADH+H+

D-Fructose

Formation of Sorbitol• Increases in activity as the glucose

concentration rises• In tissues that are not insulin-sensitive• Fructose and sorbitol in– Lens → Cataract

– Peripheral nerves → Neuropathy– Renal glomeruli → Nephropathy

Essential Fructosuria

D-Fructose

Fructo- ATPkinase

Fructose-1-P

↓_↑

It is benign and asymptomatic.

Hereditary Fructose Intolerance (Fructose Poisoning)

Fructose-1-P

↓ ↓Aldolase B Glyceraldehyde DHAP

↑

o Autosomal recessive (1:20,000 births)o Symptoms similar to excessive fructose consumption.o Sucrose & fructose must be removed from the diet.

Excessive Fructose ConsumptionFructose ↑

Fructose 1-P ↑

Pi ↓

ATP ↓

Gluconeogenesis ↓

Hypoglycemia

Protein synthesis ↓

Clotting factors & other

essential

prot

eins ↓

AMP ↑

AMP degrade

d

Hyperuricaemia

Gout

DHAP ↑

Glycerol 3-P ↑

entry into glycolysis ↑

Pyruvate ↑

Acetyl CoA ↑

Fatty acid ↑

Hypertriacyl-

glycerolaemia

Cholestrol ↑

Hypercholes-

trolemia

Atherogenic

Fructose

Fru-1-P

Glyceraldehyde

Glycerol

Glucose

Fru-6-P

DHAP

Glucose 6-P

Fru 1,6-BisP

Glycerol 3-P DHAP

Glyceraldehyde 3-P

PFK F-1,6 bis-P

HexokinaseATP

FructokinaseATP

Aldolase B

Triokinase ATP

Glycerol kinase ATP

DH

Glycogen

NADH+H+

NADTAG

pyruvate