Plays an essential role in total transketolase activity and cell proliferation in cancer cells; after transfection with anti-TKTL1 siRNA, total transketolase activity dramatically decreases and proliferation was significantly inhibited in cancer cells. Plays a pivotal role in carcinogenesis (By similarity). D-glyceraldehyde 3-phosphate + D-sedoheptulose 7-phosphate = aldehydo-D-ribose 5-phosphate + D-xylulose 5-phosphate Binds 1 Mg(2+) ion per subunit. Can also utilize other divalent metal cations, such as Ca(2+), Mn(2+) and Co(2+). Binds 1 thiamine pyrophosphate per subunit. Homodimer. Belongs to the transketolase family.