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. 2021 Jan 5;22(1):472. doi: 10.3390/ijms22010472

Figure 3.

Figure 3

Melatonin isomers (MI) production by S.cerevisiae EC1118. Chromatogram in (A) shows the melatonin transition (m/z 233.2 > 174.2) of a pure standard containing melatonin (MEL, rt 6.80) tryptophan ethyl ester (TEE, rt 6.11) both at a concentration of 2 ng/mL and internal standard (MEL OCD3, rt 6.84, m/z 236.2 > 177.2, black). Chromatograms in (B) show the superimposition of melatonin trace (m/z 233.2 > 174.2) from three different S. cerevisiae EC1118 fermentation supernatants at 24 h (blue), 48 h (red), and 72 h (green). In (B) is evident the absence of the melatonin peak that should be expected at the same retention time of its labeled analogue (rt 6.80, black). Among melatonin isomers in fermentation medium it was evidenced the presence of tryptophan ethyl ester (TEE, rt 6.06) and two isomers, named MI1 (rt 4.70) and MI2 (rt 5.6), with a not-elucidated structure.