title: Theoretical analysis of carbon-13 magnetization transfer for in vivo exchange between alpha-ketoglutarate and glutamate.
abstract: Many enzymes catalyze fast exchange between a small pool and a large pool in vivo. For example, aspartate aminotransferase catalyzes fast exchanges between alpha-ketoglutarate and glutamate and between oxaloacetate and aspartate, which can be detected using in vivo(13)C MRS while saturating alpha-carbons of the keto acids. Unlike in the traditional saturation transfer experiments studied using (31)P MRS, the tricarboxylic acid cycle intermediates alpha-ketoglutarate and oxaloacetate are below the detection limit of in vivo NMR. In this work, a theoretical analysis of the saturation transfer between alpha-ketoglutarate and glutamate catalyzed by aspartate aminotransferase was presented to examine the requirements for complete saturation of the rapidly turning over alpha-ketoglutarate pool without affecting the longitudinal magnetization of glutamate. The fast turnover of the small alpha-ketoglutarate pool also allows a quasi-steady-state approximation of its dynamic longitudinal relaxation. The theoretical analysis provides a useful guide for designing experimental methods to characterize saturation transfer processes associated with fast turning over small pools in vivo.
authors.affiliation: Molecular Imaging Branch, National Institute of Mental Health, Bethesda, MD 20892, USA. shenj@intra.nimh.nih.gov
authors.forename: Jun
authors.initials: J
authors.lastname: Shen
authors.forename: Su
authors.initials: S
authors.lastname: Xu
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis / Q000737:chemistry*; D003198:Computer Simulation; D004735:Energy Transfer; D018698:Glutamic Acid / Q000032:analysis / Q000737:chemistry*; D007656:Ketoglutaric Acids / Q000032:analysis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008280:Magnetics; D008956:Models, Chemical
chemical_list: D002247:Carbon Isotopes; D007656:Ketoglutaric Acids; D018698:Glutamic Acid