Studies on histidine-rich polypeptides from human parotid saliva

The isolation of an histidine-rich polypeptide from human parotid saliva is described. This polypeptide, termed HRP-1, contains 17% histidine. HRP-1 is a neutral molecule and is a precursor of the cationic histidine-rich polypeptides found in saliva. Results of in vitro saliva incubations suggest that breakdown of HRP-1 is enzyme mediated. Degraded species are smaller in size, more cationic in charge, and higher in histidine content. It is concluded that the many histidine-rich polypeptides in saliva are not all individual gene products and are related by a proteolytic degradation.