Radioimmunoassay for salivary carbonic anhydrase in human parotid saliva

A specific radioimmunoassay for human carbonic anhydrase (CA) VI has been developed and used to determine the concentrations of the enzyme in saliva. The assay detected as little as 200 pg of CA VI and the antibody used did not cross-react with CA II or other salivary proteins. The method showed an intra-assay variation of 8.5% and an inter-assay variation of 16.9%. The concentration in parotid saliva varied over a wide range (from 9.7 micrograms/ml to 121 micrograms/ml) with an average value of 47.0 +/- 39.2 (SD) micrograms/ml (n = 50). The mean secretion rate of CA VI from the combined parotid glands was 42.8 +/- 37.9 micrograms/min. CA VI represented about 3% of the total protein in parotid saliva.