 values of ( kcat / km)gap for triosephosphate 
 isomerase - catalyzed reactions 
 of ( r)-glyceraldehyde 3-phosphate and kcat / khpikga for reactions of the substrate pieces glycolaldehyde 
 and hpo32 have been determined for wild - type 
 and the following tim mutants : i172v , i172a , l232a , and p168a ( tim 
 from trypanosoma brucei brucei ) ; a 
 208-tgag for 208-yggs loop 7 replacement mutant ( l7rm , tim from chicken 
 muscle ) ; and , y208 t , y208s , y208a , y208f and s211a ( yeast tim ) . 
 a 
 superb linear logarithmic correlation , with slope of 1.04  0.03 , 
 is observed between the kinetic parameters for wild - type and most 
 mutant enzymes , with positive deviations for l232a and l7rm . 
 the unit 
 slope shows that most mutations result in an identical change in the 
 activation barriers for the catalyzed reactions of whole substrate 
 and substrate pieces , so that the two transition states are stabilized 
 by similar interactions with the protein catalyst . 
 this is consistent 
 with a role for dianions as active spectators , which hold tim in a 
 catalytically active caged form . 
Supplementary Material