title: 13C NMR analysis of intercompartmental flow of one-carbon units into choline and purines in Saccharomyces cerevisiae.
abstract: In Saccharomyces cerevisiae, the three-carbon of serine is normally the major one-carbon donor, although glycine and formate can substitute for serine. The second carbon of glycine enters via the glycine cleavage system in the mitochondria and can satisfy all cellular one-carbon requirements. It remains unresolved, however, as to the route by which these mitochondrial one-carbon units supply cytosolic anabolic processes. In the present work, we have used yeast mutants blocked at selected sites and 13C NMR to trace the incorporation of glycine-derived mitochondrial 5,10-methylenetetrahydrofolate into nonmitochondrial synthesis of choline and purines. Label incorporation into choline traces the methylation pathway of choline synthesis from production of serine to methylation of phosphatidylethanolamine. The active one-carbon unit of S-adenosylmethionine involved in methylation reactions originates almost solely from C3 of serine. On the other hand, flow of mitochondrial one-carbon units to 10-formyltetrahydrofolate for purine synthesis is shown to occur via both serine and formate. Formate transport accounts for at least 25% of the total, even during growth with sufficient serine to provide for the one-carbon requirements of the cell. This work shows that the synthetase function of the cytosolic C1-tetrahydrofolate synthase plays a critical role in the processing of mitochondrial one-carbon units to 10-formyltetrahydrofolate pools. In addition, this study provides evidence of two pools of glycine within the mitochondria and establishes a system of analyzing flux into the different folate derivatives.
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas, Austin 78712.
authors.forename: L B
authors.initials: LB
authors.lastname: Pasternack
authors.forename: D A
authors.initials: DA
authors.lastname: Laude
authors.forename: D R
authors.initials: DR
authors.lastname: Appling
mesh_terms: D000225:Adenine / Q000378:metabolism; D002247:Carbon Isotopes; D002794:Choline / Q000378:metabolism*; D005561:Formates / Q000378:metabolism; D005838:Genotype; D005998:Glycine / Q000378:metabolism; D006147:Guanine / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008954:Models, Biological; D011687:Purines / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D005561:Formates; D011687:Purines; C030544:formic acid; D012694:Serine; D006147:Guanine; D000225:Adenine; D002794:Choline; D005998:Glycine