BIOCHEMISTRY | Fructose galactose

Fructose

the second most common sugar in the adult diet, is ingested principally as the monosaccharide or as part of sucrose.

Fructose

is found in the diet as a component of sucrose in fruit, as a free sugar in honey, and in high-fructose corn syrup

Fructokinase

enzyme

Phosphorylation of fructose

Hexokinase

enzyme

fructose to fructose-6-phosphate

Fructokinase

enzyme

fructose to fructose-1-phosphate

aldolase B (also called fructose 1-phosphate aldolase)

enzyme

Cleavage of fructose 1-phosphate

A,B,C

Humans express three aldolases:

Aldolase A

aldolase type

found in most tissues - glycolytic

Aldolase B

aldolase type

in liver

Aldolase C

aldolase type

in brain - glycolytic

Essential fructosia

• Deficiency of fructokinase

• The enzyme is normally present in liver, pancreatic islets and kidney cortex

• Autosomal recessive

• Accumulation of fructose

Hereditary Fructose Intolerance

• Deficiency of Aldolase B

• Fructose 1-phosphate accumulates

• Depletion of inorganic phosphate (Fi), depletion of ATP

• Onset: 4-6 months,

• No treatment

glucose (aldose reductase) to sorbitol (sorbitol DH) to fructose

fructose pathway, polyol process

Liver, Ovaries, and Seminal  (they LOSe sorbitol)

they have both enzyme

(LuRKS) lens, retina, kidneys, schwann cells

only have aldolase reductase

galactokinase

enzyme

galactose to galactose 1-phosphate

Galactose-1-phosphate uridyltransferase (GALT).

enzyme

Formation of UDP-galactose

UDPhexose 4-epimerase

enzyme

Use of UDP-galactose

• Type I: Classic galactosemia - GALT deficiency

• Type Il: Galactokinase deficiency

• Type lIl: similar to Type 1 or lI

Three forms of Galactosemia