An enzyme of both the pentose phosphate pathway in all organisms and the Calvin cycle of photosynthesis.

It catalyzes two important reactions: the first reaction of the non-oxidative pentose phosphate pathway, the cofactor thiamine diphosphate accepts a 2-carbon fragment from a 5-carbon ketose, then transfers this fragment to a 5-carbon aldose to form a 7-carbon ketose.

Transketolase connects the pentose phosphate pathway to glycolysis, feeding excess sugar phosphates into the main carbohydrate metabolic pathways.

Transketolase is necessary for the production of NADPH, especially in biosyntheses, such as fatty acid synthesis by the liver and mammary glands, and for steroid synthesis by the liver and adrenal glands.

Thiamine diphosphate is an essential cofactor, along with calcium.

Transketolase is abundantly expressed in the cornea by the stromal keratocytes and epithelial cells and is reputed to be one of the corneal crystallins.

The following human genes encode proteins with transketolase activity:

TKT (transketolase)

TKTL1 (transketolase-like protein 1)

TKTL2 (transketolase-like protein 2)

The enzyme is able to bind various types of substrates, such as phosphorylated and nonphosphorylated monosaccharides including the keto and aldosugars fructose, and ribose.

This enzyme has a high specificity for hydroxyl groups of the sugars.

Transketolase activity is decreased in deficiency of thiamine.

Deficiency of thiamine in general is due to malnutrition.

Several diseases are associated with thiamine deficiency, including: beriberi, biotin-thiamine-responsive basal ganglia disease, and Wernicke-Korsakoff syndrome?

Thiamine deficiency leads to Wernicke-Korsakoff syndrome only in those whose transketolase has a reduced affinity for thiamine.

Red blood cell transketolase activity is reduced in deficiency of thiamine (vitamin B1), and may be used in the diagnosis of Wernicke’s encephalopathy and other B1-deficiency syndromes.

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