Indolicidin, a 13-residue antimicrobial peptide isolated from cytoplasmic granules of bovine neutrophils, exhibits activity against Gram-positive and Gram-negative bacteria as well as fungi. Although indolicidin is bactericidal and permeabilizes the bacterial membranes, it does not lyse the bacterial cells. We examined the effect of bactericidal concentrations of indolicidin on the morphology of Escherichia coli cells and found that it induces filamentation. Further investigations showed that indolicidin inhibits DNA synthesis in E. coli cells at concentrations at which RNA and protein synthesis are either partially affected or not affected at all. Since inhibition of DNA synthesis is also known to induce filamentation in E. coli, it appears to contribute to the antimicrobial activity of indolicidin.

ities comparable to that of IL whereas ILF exhibits only poAbstract The antimicrobial and hemolytic activities of the 13-tent antimicrobial activity without any hemolytic activity. room temperature. The peptides were checked for purity on HPLC using a reverse-phase column (Bio Rad C4 Hi-Pore RP 304, 250 ×4.6 Key words: Indolicidin; Antimicrobial activity; Hemolytic mm), using a solvent system of 0.1% aqueous TFA and acetonitrile. activity; Membrane permeabilization All the peptides were > 90% pure. However, HPLC purified peptides were used for all studies. The peptides were characterized by amino acid and sequence analyses on a LKB 4151 Alpha plus analyser and 473A Applied Biosystems gas phase sequencer, respectively.

The major carotenoid pigments of an Antarctic psychrotolerant bacterium, Sphingobacterium antarcticus, and a mesophilic bacterium, Sphingobacterium multivorum, were identified as zeaxanthin, beta-cryptoxanthin, and beta-carotene. Analysis was based on ultraviolet-visible spectroscopy, mass spectroscopy, and reversed-phase HPLC. Photoacoustic spectroscopy of intact bacterial cells revealed that the bulk of the pigments in S. antarcticus and S. multivorum was associated with the cell membrane. In vitro studies with synthetic membranes of phosphatidylcholine demonstrated that the major pigment was bound to the membranes and decreased their fluidity. The relative amounts of polar pigments were higher in cells grown at 5 degrees C than in cells grown at 25 degrees C. In the mesophilic strain, the synthesis of polar carotenoids was quantitatively less than that of the psychrotolerant strain.

Melittin, the 26-residue predominant toxic peptide from bee venom, exhibits potent antibacterial activity in addition to its hemolytic activity. The synthetic peptide of 15 residues corresponding to its C-terminal end (MCF), which encompasses its most amphiphilic segment, is now being shown to possess antibacterial activity about 5^7 times less compared to that of melittin. MCF, however, is 300 times less hemolytic. An analog of MCF, MCFA, in which two cationic residues have been transpositioned to the N-terminal region from the C-terminal region, exhibits antibacterial activity comparable to that of melittin, but is only marginally more hemolytic than MCF. The biophysical properties of the peptides, like folding and aggregation, correlate well with their biological properties.z 1999 Federation of European Biochemical Societies.

No abstract