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.
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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.
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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