Abstract: Lactoferrin (LF) shows antimicrobial activity on both Gram-negative and Gram-positive bacteria, especially the former. The antimicrobial effect improves with decrease of the iron saturation decreases. The change in pH values could affect the inhibition capability of Gram-positive bacteria but not of Gram-negative strains, while the optimum antibacterial effects are found to be pH 7.5～8.0. The bacteriostatic effects increase with higher concentration of bicarbonate, but decrease with addition of citrate and cation. Circular dichroism (CD) analysis of the secondary structure of LF showed that α-helix is transformed to β-sheet with increase of iron saturation, and the arrangement of molecular becomes better arranging in order and the structure of protein becomes more compact. DSC results indicated that the difference in the heat sensitivity between N-lobe and C-lobe is caused by the difference of the iron-binding capacity of the two lobes. The higher antibacterial activity with less iron-saturation is resulted from C-lobe.

Key words: lactoferrin, antimicrobial activity, iron saturation, circular dichroism