[Determination of nitrate reductase activity in mixed saliva]

A procedure is developed for estimation of nitrate reductase activity in saliva. Effects of pH, temperature and nature of electron donor on the enzymatic activity were studied. The maximal enzymatic activity was found at pH 6.5-7.0; heating and freezing of saliva led to loss of the enzymatic activity. Salivary nitrate reductases are of microbial origin and belong to "terminal" type of nitrate reductases. The enzyme activity varied in the interval 0.8-17.3 mmole/min per I L saliva and did not depend on human sex.