Source of neuraminidase in human whole saliva

Whole saliva specimens from eight healthy human adults were examined for neuraminidase. The presence of two types of neuraminidase in four samples out of eight was demonstrated by means of polyacrylamide gel electrophoresis and sucrose density gradient centrifugation. One type is soluble and the other an insoluble, perhaps particle-bound, enzyme. The pH optima were 5.8 for the former and 5.0 to 5.3 for the latter. However, the soluble enzyme could not be detected in the other four saliva specimens which showed low activity. A comparative study of the salivary and other neuraminidases was carried out. It was found that both salivary neuraminidases were closely similar to the enzymes in submandibular-sublingual secretions and in human liver, but not to the oral streptococcal enzymes. The results suggest that the salivary neuraminidases might originate from cells such as epithelial cells or polymorphonuclear leukocytes, or both, in the oral cavity.