which requires thiamine pyrophosphate as the cofactor in HMP pathway?

Transketolase catalyzes the transfer of a two-carbon unit from xylulose5-phosphate to ribose-5-phosphate, producing the seven-carbon ketose sedoheptulose-7-phosphate and the aldose glyceraldehyde-3-phosphate. ThusThis reaction requires two coenzymes:(a) Mg2+ (b)Thiamine diphosphate (vitamin B1) Measurement of erythrocyte transketolase and its activation by thiamine pyrophosphate provides an index of vitamin B1 nutritional status. Reference: Harper's Illustrated Biochemistry 31stedition Page nos 183-185