LEUKOCYTE MYELOPEROXIDASE AND SALIVARY LACTOPEROXIDASE - IDENTIFICATION AND QUANTITATION IN HUMAN MIXED SALIVA

Human salivary lactoperoxidase (HS-LP) is synthesized and secreted by the salivary glands, whereas myeloperoxidase (MPO) is found in PMN leu kocytes, which migrate into the oral cavity at gingival crevices. HS-L P levels vary with changes in salivary gland function, but increased n umbers of MPO-containing leukocytes indicate infection or inflammation of oral tissues. To determine the contribution of each enzyme to the peroxidase activity of mixed-saliva samples, activity was assayed at p H 5.4 with tetramethylbenzidine as the substrate, with and without the inhibitor dapsone (4,4'-diaminodiphenylsulfone). Dapsone blocked the activity of HS-LP but not MPO. The enzymes were also separated and par tially purified from the soluble portion of saliva samples and from de tergent extracts of the saliva sediment. Chromatographic properties of the proteins were similar to those of LP from bovine milk (BM-LP) and MPO from human leukocytes. The identity and amounts of the enzymes we re confirmed by the absorption spectra and by immunoblotting with anti bodies to BM-LP and human MPO. Eosinophil peroxidase (EPO), a distinct enzyme found in eosinophilic leukocytes, was not detected by chromato graphy or with antibodies to human EPO. On average, 75% of the activit y in samples from normal donors was due to MPO and 25% to HS-LP. When corrected for the lower specific activity of HS-LP in this assay, the average amount of MPO (3.6 mu g/ml) was twice the amount of HS-LP (1.9 mu g/mL). The amount of MPO corresponded to 1 x10(6) PMN leukocytes/m L of saliva. The enzymes were distributed differently: Eighty-nine per cent of the HS-LP was in the soluble portion of saliva, and 78% of the MPO was in the sediment, which contained 51% of the total activity. I n contrast to results obtained with PMN leukocytes from blood, deterge nt was not required for MPO activity to be measured in saliva, indicat ing that the enzyme was accessible to peroxidase substrates. The resul ts indicate that MPO is responsible for a large portion of peroxidase- catalyzed reactions in mixed saliva. The unique function of HS-LP may be carried out within the salivary glands, prior to secretion into the oral cavity.