9.C.6 The Mitochondrial Organic Anion Channel (MOAC) Family
The separate localization of glyoxylate cycle enzymes in the peroxisomes and the cytosol of the yeast Saccharomyces cerevisiae indicated that the peroxisomal membrane must permit the flow of metabolites between the two compartments (Antonenkov et al. 2009). The transfer of these metabolites may require peroxisomal membrane channel(s). An electrophysiological approach (reconstitution assay in lipid bilayers) allowed measurement of peroxisomal membrane channels conducting different solutes including metabolites of the glyoxylate cycle. At least two distinct channel-forming activities were detected in peroxisomal preparations (Antonenkov et al. 2009). One of these activities was highly inducible by dithiothreitol and showed large-amplitude current increments when 1M KCl was used as the bath solution. Single-channel analysis revealed that the inducible channel is anion-selective (P(Cl-/ P(K+) = 2.6; P(citrate)/P(K+) = 1.6) and displays flickering at holding potentials over + or - 30mV. The channel inducible by DTT facilitates the transfer of solutes with a molecular mass of up to 400Da, sufficient to allow the transport of glyoxylate cycle intermediates between the peroxisomal lumen and the cytoplasm.