The Pentose Phosphate Pathway & Other Pathways of Hexose Metabolism

Practice flashcards covering the biochemical importance, reactions, and clinical aspects of the Pentose Phosphate Pathway, Uronic Acid Pathway, and fructose/galactose metabolism.

Pentose Phosphate Pathway (PPP)

An alternative route for the metabolism of glucose that does not generate ATP but produces NADPH and ribose 5-phosphate.

G6PD (Glucose 6-phosphate dehydrogenase)

The first enzyme of the Pentose Phosphate Pathway; its genetic deficiency is a major cause of hemolytic anemia.

Uronic acid pathway

A metabolic route in the liver that converts glucose to glucuronic acid, ascorbic acid, and pentoses, essential for the excretion of xenobiotics.

Essential pentosuria

A rare hereditary disease where L-xylulose appears in the urine due to a deficiency in the uronic acid pathway.

Oxidative nonreversible phase

The first phase of the PPP involving the two-step dehydrogenation of G6P to ribulose 5-phosphate, producing NADPH and $CO_2$.

Nonoxidative reversible phase

The second phase of the PPP where ribulose 5-phosphate is converted into ribose 5-phosphate or glycolytic intermediates like GA3P and F6P.

Epimerase

An enzyme in the nonoxidative phase that converts ribulose 5-phosphate into xylulose 5-phosphate.

Isomerase

An enzyme that converts ribulose 5-phosphate into its aldopentose isomer, ribose 5-phosphate.

Transketolase

An enzyme that transfers a two-carbon unit from xylulose 5-phosphate to an aldose, such as ribose 5-phosphate or erythrose 4-phosphate.

Transaldolase

An enzyme that transfers a three-carbon unit from sedoheptulose 7-phosphate to GA3P to form F6P and erythrose 4-phosphate.

Glutathione reductase

A flavoprotein containing FAD that uses NADPH to reduce oxidized glutathione ($G-S-S-G$).

Glutathione peroxidase

A selenium-containing enzyme that uses reduced glutathione to remove $H_2O_2$, protecting cell membranes from oxidative damage.

UDP-glucuronate

The active form of glucuronate used for conjugating steroid hormones, bilirubin, and drugs for excretion in urine or bile.

Fructokinase

An enzyme in the liver that phosphorylates fructose to fructose 1-phosphate; it is not affected by insulin or fasting.

Aldolase B

The enzyme that cleaves fructose 1-phosphate into D-glyceraldehyde and DHAP in the liver.

Galactokinase

An enzyme that catalyzes the phosphorylation of galactose to galactose 1-phosphate using ATP.

Lactose synthase

An enzyme in the mammary gland that catalyzes the condensation of UDPGal with glucose to yield lactose.

Favism

A condition where G6PD-deficient individuals experience hemolytic anemia after consuming fava beans ($Vicia \, fava$).

Sorbitol pathway

A pathway that forms fructose from glucose; the accumulation of its intermediate, sorbitol, causes osmotic damage in tissues like the lens during diabetes.