On the dual action of ascorbate and erythorbate on rat liver lysosomes

Low concentration (0.1--1 mM) of ascorbate and erythorbate (isoascorbate) caused lipid peroxidation and lysosome labilization ("cofactor" action). In addition, they acted additively on microsomal NADPH oxidase-induced lipid peroxidation at the low concentration. The "cofactor" action, however, was dependent reciprocally on the density of lysosomes; the more dilute was the lysosomal fraction, the more susceptible the lysosomes were. On the other hand, ascorbate and erythorbate at concentration more than 1 mM inhibited microsomal NADPH oxidase-induced lipid peroxidation and lysosome labilization. Their antioxidant effect was revealed to be clear especially when the "cofactor" action was eliminated by such a basic protein as protamine. Considering that the "cofactor" action was observed only at the lower density of lysosomes and might be inhibited by physiologically occurring basic proteins, ascorbate and erythorbate may mostly act as antioxidant on lysosomes in vivo. Ascorbate- or erythorbate- induced lysosome labilization was certified to be mediated by lipid peroxidation.