Antioxidant properties of Apolipoprotein-D methionine- and selenomethioninecontaining peptides
Apolipoprotein D (ApoD), a lipocalin abundantly present in the central nervous system, has been recently shown to combat oxidative stress. This protein increases expression during Alzheimer's disease and other neurodegenerative diseases, indicating that this is one of the body's natural defences against redox events. The reducing capacity of ApoD is believed to come from Met93, which is exposed within the ligandbinding region of the protein. Purpose: We have developed nine peptides based on the three methionines within ApoD to determine the strength of reduction caused by methionine, and whether this is affected by the surrounding amino acids. In addition, selenomethionine mutants have been used in order to establish whether selenium confers a stronger redox capability than sulfur, and whether peptides containing this amino acid can be recycled to perpetuate the antioxidant cycle. Results: Initial studies have proved Met49 and SeMet49 to be highly successful reductants, with the SeMet49 peptide demonstrating extremely rapid reduction within the HPLC studies, as well as in experiments using liposomes as a model for membrane lipids. The SeMet93 is capable of bringing the peroxidation of liposomes to baseline level over a 12 hour timecourse.