A radioimmunosorbent technique for the assay of B- and C-types of carbonic anhydrase in human tissues.

A radioimmunosorbent technique for the assay of the human carbonic anhydrase isoenzymes HCA B and HCA C in tissue fluids was developed. The sensitivity of the method was 0.2 ng/ml and the precision was 5% in duplicate determinations for both enzymes. The presence in a tissue of up to 20 times higher concentrations of one isoenzyme will not interfere with the assay of the other. Haemolysates contained (mean +/- SE, n = 11) 12.1 +/- 0.52 and 1.5 +/- 0.06 mg enzyme/g Hb, and serum 0.63 +/- 0.12 and 0.2 +/- 0.02 microgram/ml of HCA B and HCA C, respectively. Pilot experiments indicated that the isoenzymes can be determined also in tissues, i.e. urine, saliva and cerebrospinal fluid, where catalytic methods previously have indicated absence of or only weak carbonic anhydrase activity. N-terminals of both enzymes were not antigenic.