Glutathione release in extracellular form by S. cerevisiae strains

Glutathione (GSH, L--glutamyl-L-cysteinyl-glycine) is the most abundant non-protein thiol compound widely present in living organisms, from prokaryotes to eukaryotes (Anderson 1998). It is synthesised intracellularly by the consecutive actions of -glutamylcysteine synthetase, feedback inhibited by GSH, and GSH synthetase. This tripeptide’s very low redox potential gives it the properties of a cellular redox buffer (Udeh and Achremowicz 1997). In living tissues, GSH plays a pivotal role in bioreduction, protection against oxidative stress, xenobiotic and endogenous toxic metabolite detoxification, enzyme activity and sulphur and nitrogen metabolism (Penninckx 2002). These characteristics make this active tripeptide an important aid and/or support for the treatment of numerous diseases, such as HIV infections, liver cirrhosis, pancreatic inflammations and aging (Wu et al., 2004). In addition, GSH is of interest in the food additive industry and sports nutrition (Lomaestro and Malone 1995). Yeasts, in particular belonging to the genus Saccharomyces, are the most commonly used microorganisms on an industrial scale for GSH fermentative production; however GSH contents of the wild-type strains are usually variable (0.1 – 1% dw) and always in intracellular form (Rollini and Manzoni 2006). The present research was aimed at obtaining GSH in extracellular form, released from cells, at high levels. Samples of S. cerevisiae (baker’s yeast) from different suppliers were tested, together with reference strains belonging to international collections. Cells were comparatively treated employing physical and chemical procedures. The best result (2.9 g/l, 90% of produced GSH in extracellular form) was achieved at 24 h reaction, employing lyophilised cells from compressed baker’s yeast. The possibility of obtaining GSH directly in extracellular form, skipping the downstream cell extraction step, represents an interesting opportunity of reducing GSH production cost and furthering the range of application and utilization of this molecule.