THE ISOLATION OF ENZYME TRANSKETOLASE FROM HUMAN ERYTHROCYTES: THE CHARACTERIZATION OF ITS QUARTERNARY STRUCTURE

Human erythrocyte transketolase (sedoheptulose-7-phosphate: D-glyceraldehyde-3-phosphate, glycolaldehyde transferase, E.C. 2.2.1.1.) has been isolated from erythrocytes with a specific activity of 59.84 U/mg. SDS-PAGE and SE-HPLC were used both as a measure of purity and as a preparative mean to obtain a higher degree of purity. Four protein bands corresponding to molecular weights of 32,000, 39,000, 43,000 and 60,000 were obtained in electrophoresis and SE-HPLC preparations. Activity measurements on the two fractions obtained from SE-HPLC that contained a monomer with the molecular weight of 32,000 and a dimeric fraction with the molecular weight of 60,000 showed that the monomeric form of the enzyme displays activity in the presence and absence of the TPP and Mg(II). This activity was measured to be 14.76 U/mg in the absence of TPP and Mg(II), and 40.24 U/mg in the presence of the cofactors. The dimeric form showed an activity of 58.84 U/mg in the presence of the cofactors.