ELECTROSTATIC INTERACTIONS BETWEEN HUMAN-LEUKOCYTE ELASTASE AND SULFATED GLYCOSAMINOGLYCANS - PHYSIOLOGICAL IMPLICATIONS

The influence of ionic strength and composition on the binding and inh ibition of human leukocyte elastase by glycosaminoglycans with variabl e degree and position of sulfation was investigated. The kinetic mecha nism of inhibition had a hyperbolic, mixed-type character with a compe titive component that was promoted by low ionic strength, reduced by p hosphate ions, and which also depended on the substrate and glycosamin oglycan structure. Enzyme binding was a cooperative phenomenon that va ried with ionic strength and composition. The inhibition patterns corr elated with the cationic character of elastase and with the distributi on of arginines on its molecular surface, most notably with residues l ocated in the vicinity of the substrate binding region. The order of a ffinity for elastase binding was chondroitin 4-sulfate < chondroitin 6 -sulfate < dermatan sulfate, iduronate-containing derivatives being su perior with respect to the glucuronate-containing counterparts. Additi onal sulfation at both the 4- and 6-positions or at the N- and 4-posit ions of the N-acetylgalactosamine moiety decidedly improved the inhibi tory efficiency. The results highlight a fundamental physiological rol e of enzyme-glycosaminoglycan interactions. In the azurophil granule o f the human polymorphonuclear neutrophil, elastase and other enzymes a re bound to a matrix of chondroitin 4-sulfate because this is the only glycosaminoglycan that simultaneously offers good binding for enzyme compartmentalization together with prompt release from the bound state at the onset of phagocytosis.