Interaction of baker's yeast transketolase modified by 2,3-butanedione with anionic and nonanionic substrates.

Baker's yeast apotransketolase modified by 2,3-butanedione binds thiamine pyrophosphate, a coenzyme of transketolase, and forms a charge transfer complex which can be identified by the CD spectrum. The enzyme retains thereby its ability to bind anionic and nonanionic substrates. The affinity of the modified enzyme for donor substrates changes insignificantly, whereas Vmax decreases 5-10-fold. The results of the study show that, although the arginine residue of the active center is not involved in substrate binding, it is essential for catalysis.