Mechanisms for the microbicidal activity of cationic proteins of human granulocytes

One oxygen-independent antimicrobial system of human granulocytes consists of granular chymotropsin-like cationic proteins possessing heat-stable microbicidal activity. For elucidation of the mode of action of the cationic protein, effects on bacterial synthesis of macromolecules, ion transport, and oxygen consumption have been studied. Inhibition of incorporation of radioactive precursors into protein, ribonulceic acid, and deoxyribonucleic acid of both Staphylococcus aureus and Escherichia coli was found concomitantly with inhibition of colony formation. Cationic protein inhibited 86Rb+ influx but did not increase the leakage of intracellular 86Rb+, indicating inhibition of energy-dependent membrane transport without a breakdown of the semipermeable character of the membrane. Oxygen consumption was inhibited. Mg2+ and Ca2+ displayed a protective effect against the microbicidal activity, indicating the operation of charge interactions between cationic protein and bacterial surface. The various effects of cationic protein were more pronounced with S. aureus than with E. coli, parallelling the microbicidal activity.