Vitamin B1 Thiamin Has A Key Role In Carbohydrate Metabolism

Thiamin has a central role in energy-yielding metabolism, and especially the metabolism of carbohydrate (Figure 45-9). Thiamin diphosphate is the coenzyme for three multi-enzyme complexes that catalyze oxidative decarboxylation reactions: pyruvate dehydrogenase in carbohydrate metabolism; a-ketoglutarate dehydro-

Glutamate residue

Vitamin K hydroquinone

Vitamin K hydroquinone

OOC CH COO I

Carboxyglutamate residue non-enzymic

CO 2

Glutamate residue

CH COO

Glutamate carbanion

CH COO

Glutamate carbanion

Vitamin K epoxide

Vitamin K epoxide

Vitamin K quinone

Vitamin K quinone

Figure 45-8. The role of vitamin K in the biosynthesis of y-carboxyglutamate.

O O h3c

Thiamin Thiamin diphosphate Carbanion

Figure 45-9. Thiamin, thiamin diphosphate, and the carbanion form.

genase in the citric acid cycle; and the branched-chain keto-acid dehydrogenase involved in the metabolism of leucine, isoleucine, and valine. It is also the coenzyme for transketolase, in the pentose phosphate pathway. In each case, the thiamin diphosphate provides a reactive carbon on the thiazole moiety that forms a carbanion, which then adds to the carbonyl group of, for instance, pyruvate. The addition compound then decarboxylates, eliminating CO2. Electrical stimulation of nerve leads to a fall in membrane thiamin triphosphate and release of free thiamin. It is likely that thiamin triphosphate acts as a phosphate donor for phosphorylation of the nerve membrane sodium transport channel.

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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