Cooperativity and flexibility of active sites in homodimeric transketolase

Here we summarize evidence for non-equivalence of tao structurally similar active sites in transketolase and other thiamine-dependent enzymes. This no n-equivalence takes place when the enzymes interact with various ligands (i nhibitors, cations, coenzyme and substrates). Data on different strains in the structure of the holotransketolase subunits are also given. The above r esults are discussed within the framework of a concept of permanent alterna tive site oscillation of the transketolase molecule in the presence and in the absence of substrate as a manifestation of a 'flip-flop' mechanism. (C) 1998 Federation of European Biochemical Societies.