Distribution of immunoreactive carbonic anhydrase III in various human tissues determined by a sensitive enzyme immunoassay method.

A sensitive sandwich enzyme immunoassay method for measurement of carbonic anhydrase III (CA-III) was established by use of purified antibodies to CA-III. The assay system consisted of polystyrene balls with immobilized antibody F(ab')2 fragments and the same antibody Fab' fragments labeled with beta-D-galactosidase from E. coli. The assay was highly sensitive and pg levels of CA-III were measureable. Coefficients of variation in within-run and between-run precision studies for serum CA-III were less than 10%. Serum CA-III levels in healthy subjects of various ages ranged from 0.8 to 24 ng/ml. Concentrations of immunoreactive CA-III in the extracts of various human tissues were also determined. Tissues composed of striated muscle contained more than 10 micrograms/mg protein of CA-III, whereas other tissues, including heart muscle, contained less than 0.5 microgram/mg protein. These results were consistent with other data showing that serum CA-III levels were raised in patients with progressive muscular dystrophy but not in those with acute myocardial infarction.