Possible transport functions in vivo for the peroxisomal NAD(H) or CoA carrier (PXN) in plants. A, PXN imports CoA against AMP to fuel fatty acid activation required for β-oxidation. B, PXN functions as redox shuttle by transferring NAD versus NADH across the peroxisomal membrane to regenerate NAD for β-oxidation, redundant to the malate/oxaloacetate shuttle via the peroxisomal and cytosolic malate dehydrogenases. C, PXN mediates the NAD uptake against AMP to provide β-oxidation with its cofactor. In Arabidopsis, the peroxisomal NADH pyrophosphatase NUDT19 might generate the counter-exchange substrate AMP for the PXN carrier via NADH hydrolysis. D, PXN exports CoA, which is released during the glyoxylate cycle to prevent an accumulation of CoA in the peroxisomal matrix. Mal, Malate; OAA, oxaloacetate; pMDH, peroxisomal malate dehydrogenase; cMDH, cytosolic malate dehydrogenase; NUDT19, a putative NADH pyrophosphatase in peroxisomes.