The Activity of Carbonic Anhydrases B and C from Human Erythrocytes and the Inhibition of the Enzymes by Copper

The catalytic activity of two isolated forms of human erythrocytic carbonic anhydrase, HCAB and HCAC, was studied at 1.6° C by means of a pH‐stat method. 80 per cent of the activity of the carbonic anhydrase with high specific activity (HCAC) was inhibited in the presence of 1.6 μM CuSO 4 , whilst the activity of the form with low specific activity (HCAB) was the same as that in a reaction medium which contained no inhibiting metallic ions. A chelating agent (EDTA), which eliminated the effect of CuSO 4 , had no effect on the enzyme activity in reaction media in which the concentration of the ions of heavy metals was below a critical level. The fact that HCAC is inhibited more effectively by copper than HCAB, was utilized in a procedure by means of which the activity of HCAC and HCAB was determined separately in solutions which contained both enzymes. The same procedure was used to determine the enzyme content of the erythrocytes, on the assumption that HCAC and HCAB in haemolysates had the same specific catalytic activity and were inhibited by CuSO 4 to the same extent as in preparations of the isolated forms of carbonic anhydrase which were used in the investigations. On the basis of results from investigations of the blood from 24 donors it was calculated that HCAC comprises 80 per cent of the activity and about 20 per cent of the carbonic anhydrase concentration in red cells. The total carbonic anhydrase activity in erythrocytes from 5 new‐born infants was about one tenth of that in the erythrocytes from adults. A high erythrocytic carbonic anhydrase activity in 2 patients with untreated pernicious anaemia was found to be the result of a parallel increase in the activity of HCAB and HCAC.