Kinetic Studies of Mouse Brain Transketolase

Abstract

The activity of transketolase in mouse brain was 5.7 nmol/min per mg protein measured by an enzyme-coupled spectrophotometric assay. The apparent Km for ribose-5-phosphate was 330 .mu.M, for D-xylulose-5-phosphate was 120 .mu.M and for thiamine pyrophosphate was 7 .mu.M. Thiamine pyrophosphate remained tightly bound to transketolase in homogenates in which it dissociated completely from another thiamine pyrophosphate-dependent enzyme, the pyruvate dehydrogenase complex. 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.