Thiamin Pyrophosphate

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Thiamin Pyrophosphate

Thiamin pyrophosphate is a coenzyme of universal occurrence responsible for transferring active aldehyde and glyoxal groups. The active component of the coenzyme is thiamin or vitamin B₁, an active nutritional factor whose deficiency causes beri-beri in man and polyneuritis is birds.

Biochemical fuction the most important reactions is which thiamin pyrophosphate participates are oxidative decarboxylation of α-keto acids, and formation of α ketols. Its role in decarboxylation of pyruvate has been known for a long time, and hence it is sometimes called cocarboxylase. The term however does not find wide usage, since carboxylase is the term reserved for enzymes which transfer a carboxyl group in substrates. Such enzymes requires biotin as the prosthetic group.

Oxidative decarboxylation of α keto acids is catalyzed by α keto acid dehydrogenases which are TPP- dependent.

In case of non – oxidative decarboxylation, the enzyme cocarboxylase is TPP- dependent and requires magnesium for it activity.

Synthesis of α ketols is catalyzed by α ketodehydrogenases and carboxylases.

Two moles of pyruvate also yield a mole acetoin.

In all these reaction the –C-2 of the thiazole ring becomes a carbonion which participates in the decarboxylation reaction of the α keto acid. The acetaldehyde group to C-2 is then accepted bythe amino group and finally transferred to other suitable acceptors.

TPP a coenzymes in alpha ketodehydrogenase and pyruvate decarboxylase.

An important reaction catalyzed by thiamin-dependent transketolase is the conversion of xylulose-5-phosphate to sedoheptulose-7-phosphate by removing a two carbon fragment and transferring it to a five carbon aldose (HMP shunt ) similarly, phosphoketolase is concerned with the metabolism of pentose sugar in microorganisms.

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