title: Tracer studies of the interconversion of R- and S-methylmalonic semialdehydes in man.
abstract: Two human subjects were given separate oral doses of sodium [2H6]isobutyrate and [methyl-2H3]thymine and the labelling patterns of urinary metabolites were determined. Ingestion of deuterated isobutyrate resulted in the excretion of 2H5-labelled S-3-hydroxyisobutyric acid, formed on the direct catabolic pathway, and of S- and R-[2H4]-3-hydroxyisobutyric acids, formed by the reduction of S- and R-methylmalonic semialdehydes respectively. Only the R-enantiomer of urinary 3-hydroxyisobutyric acid was labelled by thymine. This labelling pattern indicates a flow from S- to R-methylmalonic semialdehyde, suggesting that the R-enantiomer is the substrate of methylmalonic semialdehyde dehydrogenase.
mesh_terms: D002087:Butyrates / Q000378:metabolism; D002852:Chromatography, Ion Exchange; D003903:Deuterium; D006801:Humans; D006885:Hydroxybutyrates / Q000652:urine; D058610:Isobutyrates; D007536:Isomerism; D008297:Male; D008314:Malonates / Q000378:metabolism*; D008315:Malondialdehyde / Q000031:analogs & derivatives / Q000378:metabolism*; D013941:Thymine / Q000378:metabolism
chemical_list: D002087:Butyrates; D006885:Hydroxybutyrates; D058610:Isobutyrates; D008314:Malonates; C033319:methylmalondialdehyde; D008315:Malondialdehyde; C020380:isobutyric acid; D003903:Deuterium; C020757:3-hydroxyisobutyric acid; D013941:Thymine