Carbonic anhydrase IV activity is localized on the exterior surface of human erythrocytes

Abstract

Carbonic anhydrase (CA) cytoplasmic isozymes CA I and CA II were found in human erythrocyte membrane ghosts, when prepared at pH 5.4 and pH 7.4, but not in ghosts prepared at pH 8.2. These findings could indicate that previously reported CA activity of ghosts was owing to contamination by CA I and CA II during the preparation of the ghosts. However, using a sensitive micro-assay, CA activity was also found in ghosts prepared at pH 8.2. This activity constitutes 0.2% of the erythrocytes' total CA-activity, and originates from a membrane-associated isoform of CA, located at the exterior membrane surface. It has immunochemical and kinetic properties like those of the membrane-bound CA IV, previously isolated from kidney, lung and small blood vessels. Its function is possibly to interact with the red cell membrane anionic transport protein, band 3, for the bicarbonate/chloride exchange.

Simple methanesulfonates are hydrolyzed by the sulfatase carbonic anhydrase activity

“…hCA IV was purified, 84.7-fold with a specific activity of 742 EUmg −1 and overall yield of 17.5%. Similarly, hCA VI was purified, 69.2-fold with a specific activity of 418 EUmg −1 and overall yield of 13.2% [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] . We report here a study on the inhibitory effects of methanesulfonate derivatives and some phenolic compounds on the CA esterase activity of isoforms hCA I, II, IV and VI.…”

110 Years of the Meyer–Overton Rule: Predicting Membrane Permeability of Gases and Other Small Compounds

“…The authors proved that the intraerythrocytic carbonic anhydrase activity was high. Unfortunately, they neither checked for carbonic anhydrase IV activity localized on the exterior surface of human erythrocytes [64] nor did they add carbonic anhydrase into the external solution. Thus, it is not clear whether the process according to Equation (14) was rate-limiting.…”

Human lens carbonic anhydrases. purification and Properties

“…The small amounts of CA isozymes responsible for this low catalytic activity did not allow detailed characterization. However, our results suggest that the human lens has the same CA isozymes, as found in erythrocytes (Wistrand et al 1999) but in smaller amounts and in different proportions. CAI was found in the chromatographic fractions (Fig.…”