Kinetic studies of mouse brain transketolase.
The activity of transketolase in mouse brain was 5.7 nmol/min/mg protein measured by an enzyme-coupled spectrophotometric assay. The apparent Km for ribose-5-phosphate was 330 microM, for D-xylulose-5-phosphate was 120 microM, and for thiamine pyrophosphate was 7 microM. However, thiamine pyrophosphate remained tightly bound to transketolase in homogenates in which it dissociated completely from another thiamine pyrophosphate-dependent enzyme, the pyruvate dehydrogenase complex. These data suggest that loss of transketolase activity is likely to be a later consequence of thiamine deficiency in mammalian brain than is decreased activity of pyruvate dehydrogenase complex.
D000818:Animals; D001051:Apoenzymes / Q000378:metabolism; D001921:Brain / Q000201:enzymology*; D007700:Kinetics; D008297:Male; D051379:Mice; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D014174:Transketolase / Q000378:metabolism*
D001051:Apoenzymes; D014174:Transketolase