10-fold increase in human plasma extracellular superoxide dismutase content caused by a mutation in heparin-binding domain.

Abstract

Extracellular superoxide dismutase (EC-SOD) is a secretory SOD isoenzyme.99% of EC-SOD is anchored to heparan sulfate proteoglycans in the tissue interstitium, and 1% is located in the vasculature in equilibrium between the plasma and the endothelium.Analysis of EC-SOD in plasma samples from 604 random blood donors revealed a common (2.2%) phenotypic variant displaying 10-fold increased plasma EC-SOD content.The EC-SOD in the plasma of these individuals, collected both before and after intravenous injection of heparin, displayed a reduced heparin affinity when compared with samples from normal individuals.The specific enzymatic activity was the same as that of normal enzyme.Nucleotide sequence analyses of two of the affected subjects revealed a nucleotide exchange resulting in a substitution of kg-213 by Gly.The substitution is located in the center of the carboxyl-terminal cluster of positively charged amino acid residues, which defines the heparinbinding domain.Polymerase chain reaction-singlestrand conformational polymorphism and allele-specific polymerase chain reaction showed that all 11 affected individuals are heterozygous, carrying the same singlebase mutation.Recombinant EC-SOD containing this mutation had a reduced heparin affinity similar to that of EC-SOD C from variant persons.The high plasma activity can be explained by an accelerated release from the tissue interstitium heparan sulfate to the vasculature and should thus be accompanied by significantly reduced tissue EC-SOD activities.Extracellular superoxide dismutase (EC-SOD)' is a secretory, tetrameric, copper-and zinc-containing glycoprotein (1).In mammals, 90-99% of the EC-SOD is found in the interstitial spaces of tissues (2-4).However, the enzyme is also found in extracellular fluids and accounts for the majority of the SOD activity of plasma, lymph, and synovial fluid (4-6).A fundamental and distinguishing property of EC-SOD is its affinity for certain glycosaminoglycans such as heparin and heparan sulfate.The latter, which exists in the glycocalyx of cell surfaces and in connective tissue matrix, appears to be the most * This study was supported by Grant 9204 from the Swedish Natural Science Research Council.The costs of publication of this article were defrayed in part by the payment of page charges.This article must therefore be hereby marked "aduertisement" in accordance with 18 U.S.C.Section 1734 solely to indicate this fact.The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) 502947.