Abstract
Abstract Lysosomal granules from rabbit neutrophilic leukocytes contain an enzyme that cleaves the fifth component of human complement (C5) into chemotactically active fragments. The enzyme cleaves C5, but not the third component of complement, into chemotactically active fragments of variable molecular weights, depending upon conditions of incubation. One fragment consistently behaves in ultracentrifugation and gel filtration similar to the reference standard cytochrome c. The amount of chemotactic activity generated by interaction of the lysosomal granule lysate and C5 is a function of concentrations of C5 and lysate, as well as duration of incubation. The C5-cleaving enzyme of neutrophil lysosomal granules has a neutral pH optimum for activity. Based upon gel filtration, it has an estimated molecular weight of 35,000, is inhibited by esters bearing basic amino acids, is susceptible to inhibition by ε-amino caproic acid and in varying degree is susceptible to action of soybean trypsin inhibitor and EDTA. The presence in the neutrophil of an enzyme capable of cleaving C5 into chemotactically active fragments may reflect the potential for the neutrophil to exacerbate in a non-immunologic manner the acute inflammatory process once it is underway.
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