Discrimination byparacoccus denitrificans between (6-13C)glucose and (1-13C)glucose as carbon substrates for growth: An investigation using gas chromatography/mass spectrometry

A study on the biosynthesis of hygrophorone B(12) in the mushroom Hygrophorus abieticola reveals an unexpected labelling pattern in the cyclopentenone moiety

The hitherto unknown natural formation of hygrophorones, antibacterial and antifungal cyclopentenone derivatives from mushrooms, was investigated for hygrophorone B(12) in Hygrophorus abieticola Krieglst. ex Gröger & Bresinsky by feeding experiments in the field using (13)C labelled samples of D-glucose and sodium acetate. The incorporation of (13)C isotopes was extensively studied using 1D and 2D NMR spectroscopy as well as ESI-HRMS analyses. In the experiment with [U-(13)C6]-glucose, six different (13)C2 labelled isotopomers were observed in the 2D INADEQUATE spectrum due to incorporation of [1,2-(13)C2]-acetyl-CoA. This labelling pattern demonstrated that hygrophorone B(12) is derived from a fatty acid-polyketide route instead of a 1,4-α-D-glucan derived anhydrofructose pathway. The experiment with [2-(13)C]-acetate revealed an unexpected incorporation pattern in the cyclopentenone functionality of hygrophorone B(12). Four single-labelled isotopomers, in particular [1-(13)C]-, [2-(13)C]-, [3-(13)C]-, and [4-(13)C]-hygrophorone B(12), were detected that showed only half enrichment in comparison to the respective labelled alkyl side chain carbons. This labelling pattern indicates the formation of a symmetrical intermediate during hygrophorone B(12) biosynthesis. Based on these observations, a biogenetic route via a 4-oxo fatty acid and a chrysotrione B homologue is discussed.

Network flux analysis: impact of 13C-substrates on metabolism in Arabidopsis thaliana cell suspension cultures

The aim of this study was to test the assumption that (13)C-enrichment of respiratory substrate does not perturb metabolism. Cell suspension cultures of Arabidopsis thaliana were grown in MS medium containing unlabelled glucose (with (13)C at natural abundance), 100% [1-(13)C]glucose, 100% [U-(13)C(6)]glucose or 10% [U-(13)C(6)]glucose plus 90% unlabelled glucose. There was no significant difference in the metabolism of [U-(14)C]glucose between the cultures. Similarly, the pattern of (14)CO(2) release from specifically labelled [(14)C]-substrates was unaffected. Principal component analysis of (13)C-decoupled (1)H NMR metabolite fingerprints of cell extracts was unable to discriminate between the different culture conditions. It is concluded that (13)C-enrichment of the growth substrate has no effect on flux through the central pathways of carbon metabolism in higher plants. This conclusion supports the implicit assumption in metabolic flux analysis that steady-state (13)C-labelling does not perturb fluxes through the reactions of the metabolic network it seeks to quantify.