Determination of Uric Acid, Tyrosine, Tryptophan, and Protein in Whole Human Parotid Saliva by Ultraviolet Absorption Spectrophotometry

¹ Laboratory of Biochemistry, National Institute of Dental Research, Bethesda, Maryland, and Department of Biochemistry, School of Medicine, Howard University, Washington, D.C.

1. Intact undeproteinized samples of whole human parotid saliva were analyzed for uric acid, protein, tyrosine, and tryptophan by chemical and ultraviolet absorption technics.

2. A simple, rapid method was devised for the simultaneous determination of uric acid, protein, tyrosine, and tryptophan in as little as 0.6-ml samples.

3. The relation between the chemical (X) and spectrophotometric (Y) determinations for tyrosine is Y = 0.92 X + 0.09, with a correlation coefficient of 0.97. The fitted line for tryptophan is described by Y = 0.94 X ± 0.71, with a correlation coefficient of 0.86. Little, if any, tryptophan appeared to reside in the ultrafiltrate fraction of the parotid fluid, whereas tyrosine peptides may be present.

4. Only 40 per cent of the Lowry-positive material of the parotid fluid absorbed in the ultraviolet and appeared to reside in the TCA-precipitate fraction.

5. Human parotid saliva was found to contain approximately 2.5 mg. per cent uric acid.