SCHEME 1.

Reductive sulfate assimilation pathway in bacteria and its relations with the nitrogen and carbon assimilation pathways. Enzyme names are shown in boldface with the exception of SAT and OASS that are shown in red. Modulation of enzyme or transcriptional activity is shown with blue arrows; cysteine feedback inhibits the activity of SAT; SAT inhibits OASS activity; N-acetylserine, the product of spontaneous O-N transfer of the acetyl group of OAS, induces the transcription of the cysteine operon. Abbreviations used are as follows: ATPS, ATP sulfurylase; APSK, 5′-phosphosulfate kinase; PAPS ST, 3′-phosphoadenosine 5′-phosphosulfate sulfotransferase; NADPH-SR, NADPH-dependent sulfite reductase; PGDH, d-3-phosphoglycerate dehydrogenase; PSAT, 3-phosphoserine aminotransferase; PSP, 3-phosphoserine phosphatase; GluDH, glutamate dehydrogenase.