Transformation of Free and Dipeptide-Bound Glycated Amino Acids by Two Strains of Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae transforms branched-chain and aromatic amino acids into higher alcohols in the Ehrlich pathway. During microbiological culturing and industrial fermentations, this yeast is confronted with amino acids modified by reducing sugars in the Maillard reaction (glycation). In order to gain some preliminary insight into the physiological "handling" of glycated amino acids by yeasts, individual Maillard reaction products (MRPs: fructosyllysine, carboxymethyllysine, pyrraline, formyline, maltosine, methylglyoxal-derived hydroimidazolone) were administered to two strains of S. cerevisiae in a rich medium. Only formyline was converted into the corresponding a-hydroxy acid, to a small extent (10%). Dipeptide-bound pyrraline and maltosine were removed from the medium with concomitant emergence of several metabolites. Pyrraline was mainly converted into the corresponding Ehrlich alcohol (20-60%) and maltosine into the corresponding a-hydroxy acid (40-60%). Five specific metabolites of glycated amino acids were synthesized and characterized. We show for the first time that S. cerevisiae can use glycated amino acids as a nitrogen source and transform them into new metabolites, provided that the substances can be transported across the cell membrane.