title: Changes in cysteine and O-acetyl-L-serine levels in the microalga Chlorella sorokiniana in response to the S-nutritional status.
abstract: We analyzed the effects of deprivation and subsequent restoration of sulphate (S) in the nutrient solution on cysteine (Cys) and O-acetyl-L-serine (OAS) levels in Chlorella sorokiniana (211/8k). The removal of S from the culture medium caused a time-dependent increase in O-acetyl-L-serine(thiol)lyase (OASTL) activity and a decrease in soluble proteins content. The protein gel blot analysis was used to show that OASTL isoforms are located in the chloroplast and in the cytoplasm of S-starved cells. S-deprivation caused a decrease in the intracellular levels of Cys and glutathione (GSH) and an increase in serine (Ser) and OAS, reflecting an imbalance between sulphur and nitrogen assimilation. Re-supplying of sulphate to S-starved cells produced a decrease in OAS levels and concomitant rapid increase in Cys and GSH concentrations. The simultaneous addition of OAS and sulphate to S-starved cells did not further increase the concentration of Cys, suggesting the existence of a threshold level of intracellular Cys that is independent of the cellular concentration of OAS. Our findings that OAS is stored during S-starvation and that its quick decrease appears to be coupled with the increase of Cys levels upon re-supply of sulphate, imply that the central role that these two compounds play is in the regulation of sulphur-assimilating enzymes in response to the S status of the cell.
authors.affiliation: Dipartimento delle Scienze Biologiche, Università di Napoli Federico II, Via Foria 223, I-80139 Napoli, Italy. simona.carfagna@unina.it
authors.forename: Simona
authors.initials: S
authors.lastname: Carfagna
authors.forename: Giovanna
authors.initials: G
authors.lastname: Salbitani
authors.forename: Vincenza
authors.initials: V
authors.lastname: Vona
authors.forename: Sergio
authors.initials: S
authors.lastname: Esposito
mesh_terms: D003545:Cysteine / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D058086:Microalgae / Q000378:metabolism*; D012694:Serine / Q000378:metabolism*; D013431:Sulfates / Q000378:metabolism
chemical_list: D013431:Sulfates; D012694:Serine; D005978:Glutathione; D003545:Cysteine