Purification and Amino Acid Analysis of Human Parotid Saliva Lysozyme

Lysozyme from human parotid saliva was purified to the point where it was judged, by the criteria of ultracentrifugation and disk electrophoresis, to be homogeneous. The parotid lysozyme had a specific activity 3.5 times greater than that of hen egg-white lysozyme and a composition that was different, especially in regard to tyrosine, serine, and glutamic acid content. The molecular weight was determined to be around 14,300. When tryptophan residues were modified with N-bromosuccinamide, no lytic activity was found, which indicates that the tryptophan residues may play an important role in the maintenance of the parotid lysozyme activity.