Carbonic anhydrase activity of intact carbonic anhydrase II-deficient human erythrocytes.

Intact erythrocytes from subjects with deficiency of blood carbonic anhydrase (CA) II and from normal subjects were assayed for enzyme activity by use of an 18O exchange technique in a solution containing 25 mM (CO2 + NaHCO3) plus 125 mM NaCl. At 25 degrees C and pH 7.4, the catalyzed reaction velocity was 0.32 +/- 0.04 M/s for the CA II-deficient and 1.60 +/- 0.12 M/s for the normal cells, a ratio of 1:5. Under the same conditions at 37 degrees C the relative difference between the CA II-deficient and normal cells was much less: the velocity for the CA II-deficient cells was 0.84 +/- 0.07 M/s and for the normal cells 1.60 +/- 0.32 M/s, a ratio of 1:1.9. Results were comparable for the hemolysates with the NaHCO3 reduced to 85 mM (the corresponding intracellular concentration): at 25 degrees C CA II-deficient cells had a velocity of 0.36 +/- 0.01 M/s compared with 1.12 +/- 0.04 M/s for the normal cells, a ratio of 1:3.1. At 37 degrees C again the relative difference between hemolysates from CA II normal and deficient cells was much less: the CA II-deficient cells had a reaction velocity of 1.17 +/- 0.22 M/s vs. 2.60 +/- 0.36 M/s for the normal cells, a ratio of 1:2.2. The greater fractional reduction of enzyme velocity of CA II-deficient cells at 25 degrees C compared with 37 degrees C appears to be explained by a greater chloride inhibition of the presumed CA I at the lower temperature.(ABSTRACT TRUNCATED AT 250 WORDS)