Abstract: A composition comprising a vinylpyridine-styrene-butadiene copolymer and at least one amino acid selected from the group consisting of proline, leucine, isoleucine, homoserine, valine, .alpha.-aminobutyric acid, .gamma.-aminobutyric acid, citrulline, lysine, ornithine, arginine, glutamic acid, aspartic acid, and salts of these amino acids. The composition may optionally contain sulfur and/or sulfur donor.