Angiotensin II Generation at the Cell Surface of Activated Neutrophils: Novel Cathepsin G-Mediated Catalytic Activity That Is Resistant to Inhibition

Human neutrophils express inducible, catalytically active cathepsin G on their cell surface. Herein, we report that membrane-bound cathepsin G on intact neutrophils has potent angiotensin II-generating activity. Membrane-bound cathepsin G on activated neutrophils 1) converts both human angiotensin I and angiotensinogen to angiotensin II; 2) expresses angiotensin II-generating activity equivalent to 8.6 +/- 2.3 (+/-SD) x 10(-18) mol of free cathepsin G (5.2 +/- 1.4 x 10(6) molecules)/cell; and 3) has similar high affinity for angiotensin I compared with free cathepsin G (Km = 5.9 x 10(-4) and 4.6 x 10(-4) M; k(cat) = 4.0 and 2.0/s, respectively). In marked contrast to soluble cathepsin G, membrane-bound enzyme was substantially resistant to inhibition by plasma proteinase inhibitors and converted angiotensin I to angiotensin II even in undiluted plasma. There was a striking inverse relationship between inhibitor size and its effectiveness against membrane-bound cathepsin G activity. Alpha1-antichymotrypsin was a markedly ineffective inhibitor of membrane-bound enzyme (IC50 = 2.18 microM and 1.38 nM when tested against 1 nM membrane-bound and free cathepsin G, respectively). These data indicate that membrane-bound cathepsin G expressed on neutrophils is an inducible and mobile angiotensin II-generating system that may exert potent local vasoactive and chemoattractant properties at sites of inflammation.