Erythrocytes carbonic anhydrases

Human carbonic anhydrase II, found primarily in the erythrocyte, is the prototypical member of the family of carbonic anhydrases and has been extensively reviewed (Pocker and Sarkanen, 1978 Lindskog, 1983, 1986 Silverman and Lindskog, 1988). Within the erythrocyte carbonic anhydrase II hydrates CO2 to form bicarbonate ion plus a proton via tandem chemical processes (Silverman and Lindskog, 1988) (Scheme 2). Most of the carbon dioxide generated during the process of respiration requires this carbonic anhydrase Il-catalyzed event for transport out of the cell. The resultant protons of CO2 hydration are taken up by His-146)8, His-122a, and the amino terminus of the a subunits of the hemoglobin tetramer. As a reference. Scheme 3 outlines the interconversions... 

In vitro studies indicated that dorzolamide binds strongly to erythrocyte carbonic anhydrase CA II and very weakly to CA I. The desethyl metabolite also binds to both CA I and CA II, but has less affinity for CA II and is considerably less selective for CA II than dorzolamide. 

K. K. Kannan, I. Vaara, B. Notstrand, S. Lovgren Borell, K. Fridborg, M. Petef (1977). Structure and function of carbonic anhydrase comparative studies of sulfonamide binding to human erythrocyte carbonic anhydrases B and C. In G. C. K. Roberts (Ed.). Drug Action at the Molecular Level. Baltimore University Park Press, pp. 73-91. 

Fig. 17. Idealized drawing of the main chain folding of human erythrocyte carbonic anhydrase C (HCAC). The helices are represented by cylinders and the pleated sheet strands are drawn as arrows in the direction from amino to carboxyl end. The ball supported on three histidyl residues represents the zinc ion (after Liljas et a/.147) Kannan et a/.148))...

Crystal structure of human erythrocyte carbonic anhydrase B. Three-dimensional structure at a nominal 2.2-A resolution Proc. Nat. Acad. Sci. USA 72, 51-55 (1975). 

Pocker, Y., and Meany, J. E. The catalytic versatility of erythrocyte carbonic anhydrase. 

Figure 2. SDS gel electrophoresis of the products of partial cystine cleavage for several test proteins. A. molecular weight standards, B. yeast alcohol dehydrogenase. C. P-lactoglobulin, D. hen egg lysozyme, E. ovalbumin, F. calf fetal serum fetuin. Molecular weight standards are indicated by arrows on the left side of the gel and are bovine serum albumin (66,300), bovine liver glutamate dehydrogenase (55,400), porcine muscle lactate ddiydiogenase (36,500), bovine erythrocyte carbonic anhydrase (31,000), soybean trypsin inhibitor (21,500), hen egg lysozyme (14,400), bovine lung aprotinin (6,000), unresolved bovine pancreatic insulin A and B chains.

One of the most important discoveries concerning the biological role of zinc occurred in 1940 when Keilin and Mann showed that zinc is an essential compound of erythrocyte carbonic anhydrase, an enzyme cata-lytically involved in the transport of CO2 in blood (6). Following the 70-year interval between the initial recognition of a metabolic zinc deficiency and the characterization of the first zinc metalloenzyme, there was a period of about 15 years before the second zinc enzyme was identified. In 1955, Vallee and Neurath reported that carboxypeptidase A from bovine pancreas contained 1 g-atom Zn per mol of protein and was essential to the function of the enzyme (7). The presence of zinc in carbonic anhydrase and carboxypeptidase A indicated that a primary role of zinc would be to function in zinc metalloenzymes (62). However, it seemed unhkely that disrupting the activity of carboxypeptidase A or carbonic anhydrase would have profound eflFects on growth. 

Abbreviations are HC, hemocyanin from Helix pomatiar IG, nonspecific human y-im-munogiobulin AD, alcohol dehydrogenase from yeast Hb, human adult carbonmonoxy-hemoglobin CA, human erythrocyte carbonic anhydrase B and LY, hen egg-white lysozyme. The numbers next to the abbreviations give the molecular weights in units of thousands of Daltons. The relaxation rate of the protein-free solvent is indicated by the horizontal dashed line. After Ref. 7. 

Abbreviations are LY, hen egg-white lysozyme CON A, demetallized concanavalin A TP, demetallized porcine trypsin tRNA, nonspecific yeast transfer ribonucleic acid CA, human erythrocyte carbonic anhydrase B Hb, human adult carbonmonoxyhemo-globin AP, E. coli alkaline phosphatase TF, demetallized human transferrin IG, human nonspecific -/-immunoglobulin AD, alcohol dehydrogenase from yeast CP, human ceruloplasmin HC1 / 20, l/IO(L), 1/10(0, 1/2, 1/1, various states of association of Helix pomatia hemocyanin. Dashed line m>calculated using Equation 3 with no adjustable parameteis, using the viscosity of pure water to compute v . The proteins were assumed spherical, and a 3J-A hydration layer was included in computing the hydrodynamic radii. After Ref. 7. 

Kannan, K. K., Notstrand, B., Fridborg, K., Lovgren, S., Ohlsson, A., and Petef, M., 1975. Crystal structure of human erythrocyte carbonic anhydrase B Three-dimensional structure at a nominal 2.2-A resolution. Proc. Natl. Acad. Sci. U.S.A. 72 51 — 55. 

Human erythrocyte carbonic anhydrase is a single polypeptide chain with 259 amino acid residues [78]. 

Carbonic Anhydrase.—Strandberg and his colleages" have calculated a 2 A resolution electron-density map of human erythrocyte carbonic anhydrase C. A polypeptide chain of 258 amino-acid residues is indicated, and two sequenced fragments have been fitted in positions 1—88 and 224— 258. The structure has a gross shape of 41 x 41 x 47 A and is built essentially of three layers. Seven distorted sections of right-handed a-helix are in the surface layers. In contrast the middle layer is an extensive mainly antiparallel pleated sheet structure with a total twist of 220° and comprising 37% of the total residues. There are aromatic regions between the central sheet and the surface layers. 

Ekinci, D. Beydemir, S. Kufrevioglu, O.I. (2007). In vitro inhibitory effects of some heavy metals on human erythrocyte carbonic anhydrases. Journal of Enzyme Inhibition and Medicinal Chemistry, 22,745-750. 

---