Capturing Metabolite Channeling in Metabolic Flux Phenotypes

Metabolite channeling, also known as substrate channeling, the process by which intermediates in metabolic pathways are passed from enzyme to enzyme without equilibration with the cellular medium, is thought to be important in the organization and regulation of metabolism (Agius and Sherratt, 1997). The process is difficult to study noninvasively, particularly in the highly connected network of central metabolism, but since channeling can provide alternative pathways its occurrence may leave a footprint in the 13C-labeling datasets that are now used for the steady-state metabolic flux analysis (MFA) of central metabolism in heterotrophic and mixotrophic plant tissues (Ratcliffe and Shachar-Hill, 2005, 2006; Libourel and Shachar-Hill, 2008; Schwender, 2008; Allen et al., 2009; Kruger and Ratcliffe, 2009). It is shown here, using existing 13C-labeling data for Arabidopsis (Arabidopsis thaliana) cell suspensions (Williams et al., 2008, 2010), that well-defined channeled fluxes can be detected in glycolysis and the tricarboxylic acid (TCA) cycle using steady-state MFA.