Unravelling Saccharomyces cerevisiae biosynthethic pathways of melatonin, serotonin and hydroxytyrosol  by UPLC-HRMS Isotopic labelling analysis

Abstract

The main objective is to unravel the yeast biosynthetic pathways for MEL, SER and HT by using the respective labelled amino acids precursors: 15N2-L tryptophan and 13C-tyrosine.
The alcoholic fermentation experiments are performed with two different commercial S cereviseae yeasts using synthetic must with the addition of the labelled compounds and the bioactive compounds were followed during the fermentation process. Six biological replicates of the fermentations were considered. MEL, SER and HT were analysed by UHPLC coupled to High Resolution Mass Spectrometry (HRMS). Accurate mass determination allowed to unequivocally distinguishing labelled and unlabelled compounds. The analytical determination was performed using external calibration curves with 10 points, which were freshly prepared at every analytical session. Potential intermediates in the synthesis of MEL are detected as labelled metabolites following a time sequence that fits with the pathway described for the synthesis of MEL in mammals. At day 3 all the initial 15N2 L-TRP has been consumed. However, L-TRP as such was detected despite it was not added to the fermentation medium, thus demonstrating de novo tryptophan formation which can be used to synthetize MEL thereafter. Similarly, the results obtained in the fermentation carried out with 13-C TYR verify that HT is formed both from labelled tyrosine and from intermediates of the Erlich pathway.