Demonstration of citrate synthase in non-glyoxysomal peroxisomes

Abstract

Non-glyoxysomal peroxisomes were isolated from potato tubers, young pea leaves, mung bean hypocotyls, and avocado mesocarp. The peroxisomal fractions exhibited citrate synthase activity but mitochondrial contamination was demonstrable only in those fractions isolated from mung bean hypocotyls and avocado mesocarp. During hydroxylapatite chromatography, the citrate synthase activity of the peroxisomal fractions (pfCS) from potato tubers and pea leaves eluted at a phosphate concentration higher than that required to elute the citrate synthase activity of the corresponding mitochondrial fractions (mfCS). The pfCS and mfCS also differed in their sensitivities towards 5,5′-dithiobis(2-nitrobenzoic acid) and palmitoyl-CoA. The sensitivity of the pfCS corresponded to that of the glyoxysomal citrate synthase isoform from sunflower cotyledons. The pfCS of mung bean hypocotyls and avocado mesocarp separated in two fractions during hydroxylapatite chromatography. One fraction showed chromatographic behavior and responded to 5,5′-dithiobis(2-nitrobenzoic acid) and palmitoyl-CoA like the pfCS of potato tubers and pea leaves; the other fraction exhibited properties identical with those of the corresponding mfCS. Therefore, the latter activity only appears to be due to the mitochondrial contamination of the peroxisomal fractions from mung bean hypocotyls and avocado mesocarp. The results demonstrate that not only glyoxysomes but also non-glyoxysomal peroxisomes possess a citrate synthase isoform.