Purification of glutathione S‐transferase from lean pork muscle and its reactivity with some lipid oxidation products

Soluble glutathione S‐transferase was isolated from lean pork meat by S‐hexylglutathione Sepharose 6B. A single form of the enzyme with a subunit molecular weight of 24 800, a pH optimum of 6.2 and an isoelectric point of 7.6 accounted for the majority of the transferase activity. The pure enzyme is stable upon storage at pH 6, and has a relatively low K_m (87 μM) for glutathione. Substrate specificity suggests membership of class Pi. Glutathione S‐transferase was able to reduce certain primary products of lipid oxidation. Linoleic acid hydroperoxides, for example, were converted to their corresponding hydroxides (specific activity = 260 nmol min⁻¹ mg⁻¹). The transferase could also inactivate secondary products of lipid oxidation. Trans,trans‐2, 4‐decadienal, which results from breakdown of lipid hydroperoxides, was chosen as an example of this class. A high specific activity (1400 nmol min⁻¹ mg⁻¹) was found for conjugation of the dienal with glutathione. It is suggested that endogenous glutathione S‐transferase functions as an antioxidant in stored muscle food by removing some of the reactive products that propagate the oxidation of lipids.