Representative examples of nonenzymatic sugar interconversions modulated by amino acids.

Product formation time courses obtained at 70°C from 100 μM substrate in the presence of different subgroups of amino acids (at a total concentration of 400 μM) are shown for different prototypic reactions: diverse transformations accelerated by the sulfur-containing amino acids cysteine and methionine, some of which are negatively affected by at least another group of amino acids (top 3 panel rows); F1,6BP dephosphorylation, enhanced by negatively charged amino acids, with antagonistic effects from positively charged amino acids (fourth set of panels); a pentose-phosphate isomerization, where the role of cysteine and methionine is actually as inhibitors (bottom panel row). Asterisks indicate reaction rates that were significantly different—either higher (green) or lower (red)—than in the aqueous control without amino acids (last column of panels) (Wilcoxon rank sum test, p = 0.1). “All mixed” stands for samples containing all 20 amino acids at a total concentration of 400 μM (i.e., 20 μM each). Data points shown in gray (N = 3 independent experiments) (see S1 Data).

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