Contaminating peptides widely present in ion-exchanged water, reagents, experimental implements and natural sample

Ion-exchanged water, various reagents, experimental implements and natural sample have been found to be widely contaminated by certain kinds of peptides, whose molecular weights are between 1000 and 6000 daltons. An amino acid analysis showed them to contain serine, glycine and alanine as the three major amino acid components, which constitute about 50% of the total amino acid in the fractions of the contaminants. Ornithine is also commonly abundantly present in the contaminants. The significance of the presence of ornithine and the origin of the contaminants are discussed.