The concentration of extracellular superoxide dismutase in plasma is maintained by LRP-mediated endocytosis

In this study, we show that human extracellular superoxide dismutase (EC-SOD) binds to low-density lipoprotein receptor-related protein (LRP) This interaction is most likely responsible for the removal of EC-SOD from the blood circulation via LRP expressed in liver tissue The receptor recognition site was located within the extracellular matrix-binding region of EC-SOD This region encompasses the naturally occurring Arg213Gly amino acid substitution, which affects the affinity of EC-SOD for ligands in the extracellular space Interestingly, the binding between LRP and Arg213Gly EC-SOD was significantly reduced, thus clarifying the observation that hetero- or homozygous carriers present with a significant increase in EC-SOD in their blood On the basis of our results, we speculate that EC-SOD synthesized locally in tissues diffuses slowly into the circulation, from where it is removed by binding to LRP present in the liver The interaction between LRP and EC-SOD is thus likely to be important for maintaining redox balance in the circulation (C) 2010 Elsevier Inc All rights reserved