The effects of cationic proteins of rabbit polymorphonuclear leukocyte lysosomes on the respiratory activity of liver mitochondria

Rapid membrane permeabilization and inhibition of vital functions of gram-negative bacteria by bactenecins

Bactenecins are a class of arginine-rich antibacterial peptides of bovine neutrophil granules. Two bactenecins with approximate molecular weights of 5,000 and 7,000 designated Bac5 and Bac7, respectively, exert in vitro a potent bactericidal activity toward several gram-negative bacteria (R. Gennaro, B. Skerlavaj, and D. Romeo, Infect. Immun. 57:3142-3146, 1989). We have now found that this activity shows an inverse relationship to the ionic strength of the medium and is inhibited by divalent cations and greatly potentiated by lactoferrin. Under conditions supporting marked bactericidal activity, the two peptides cause a rapid increase in the permeability of both the outer and inner membranes of Escherichia coli, as shown by unmasking of periplasmic beta-lactamase and of cytoplasmic beta-galactosidase. In addition, the two bactenecins inhibit the respiration of E. coli and Klebsiella pneumoniae but not of Bac5- and Bac7-resistant Staphylococcus aureus. Furthermore, they induce a drop in ATP content in E. coli, K. pneumoniae, and Salmonella typhimurium and a marked decrease in the rates of transport and incorporation of [3H]leucine and [3H]uridine into E. coli protein and RNA, respectively. In general, all these effects become evident within 1 to 2 min and reach their maximal expression within about 5 min. Overall, these data strongly suggest that the decrease in bacterial viability is causally related to the increase in membrane permeability and the subsequent fall in respiration-linked proton motive force, with the attendant loss of cellular metabolites and macromolecular biosynthesis ability.

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.