[Quaternary structure of transketolase from rat liver].

The quaternary structure of immobilized rat liver transketolase was studied. It was shown that the individual subunits of the enzyme are active in their specific activity do not differ from the dimeric form of the enzyme. The quaternary structure stabilizes the coenzyme binding to the protein; thiamine pyrophosphate is split off from the choloenzyme only upon destruction of the quaternary structure. The hybrid dimers formed by the subunits of transketolase from rat liver and baker's yeast were obtained. Their formation requires the presence of the coenzyme and Ca2+ in the medium. No reassociation of the rat liver transketolase subunits into a dimer was shown. It was assumed that in vivo the subunits of rat liver transketolase do not exist in a free state and their association into dimers occurs immediately after completion of the polypeptide chain biosynthesis in the presence of thiamine pyrophosphate.