Bio Chemistry

BIOCHEMISTRY 3(2+1)

Lesson 21 : Pentose Phosphate Pathway or HMP Shunt

Non-oxidative phase

The pentose phosphate pathway's Nonoxidative phase(Figure)

Reactants	Products	Enzymes
ribulose 5-phosphate	? ribose 5-phosphate	Ribulose 5-Phosphate Isomerase
ribulose 5-phosphate	? xylulose 5-phosphate	Ribulose 5-Phosphate 3-Epimerase
xylulose 5-phosphate + ribose 5-phosphate	? glyceraldehyde 3-phosphate + sedoheptulose 7-phosphate	transketolase
sedoheptulose 7-phosphate + glyceraldehyde 3-phosphate	? erythrose 4-phosphate + fructose 6-phosphate	transaldolase
xylulose 5-phosphate + erythrose 4-phosphate	? glyceraldehyde 3-phosphate + fructose 6-phosphate	transketolase

Dietary pentose sugars derived from the digestion of nucleic acids may be metabolized through the pentose phosphate pathway, and the carbon skeletons of dietary carbohydrates may be converted into glycolytic/gluconeogenic intermediates.

One of the uses of NADPH in the cell is to prevent oxidative stress. It reduces glutathione via glutathione reductase, which converts reactive H2O2 into H2O by glutathione peroxidase. If absent, the H2O2 would be converted to hydroxyl free radicals by Fenton chemistry, which can attack the cell.

In a significant step, erythrocytes generate, through the pentose phosphate pathway, a large amount of NADPH used in the reduction of glutathione