Determination of salivary peroxidase activity in human mixed whole saliva

Mixed whole saliva contains salivary peroxidase (SPX) and myeloperoxidase (MPO), thus it is important to discriminate between the two peroxidases in order to understand their functions in the oral cavity. We developed a method to measure SPX activity in mixed whole saliva using an oxygen electrode. According to our results, when 50% of the peroxidase activity in saliva was due to MPO, determined using a typical substrate for peroxidase guaiacol, almost all oxygen evolved was due to SPX. We propose that measurement of H2O2-dependent oxygen evolution is a useful method for determining SPX activity in whole saliva.