Carbonic anhydrase human

Fig. 11.37 Free energy profile for the nucleophilic attack of water on CO2 (a) in aqueous solution and (b) in the enzyme carbonic anhydrase. (Graphs redrawn from Aqvist J, M Fothergill and A Warshel 1993. Computer Simulai of the COj/HCOf Interconversion Step in Human Carbonic Anhydrase I. Journal of the American Chemical Society 115 631-635.)...

Aqvist J, M FothergiU and A Warshel 1993. Computer Simulation of the CO2/HCO3 Interconversi Step in Human Carbonic Anhydrase I. Journal of the American Chemical Society 115 631-635. 

Gruneberg S, Stubbs MT, Klebe G. Successful virtual screening for novel inhibitors of human carbonic anhydrase strategy and experimental confirmation. J Med Chem 2002 45 3588-602. 

Grtineberg S, Wendt B, Klebe G. Subnanomolar inhibitors from computer screening a model study using human carbonic anhydrase II. Angew Chem Int Ed Engl 2001 40 389-393 Angew Chem 2001 113 404-8. 

B34. Brady, H. J. M., Sowden, J. C Edwards, M., Lowe, N., and Butterworth, P. H. W Multiple GF-1 binding sites flank the erythroid specific transcription unit of the human carbonic anhydrase I gene. FEBS Lett. 257,451-456 (1989). 

Stanton and Merz studied the reaction of carbon dioxide addition to zinc hydroxide, as a model for zinc metallo-enzyme human carbonic anhydrase IIJ 36. It was shown that the LDA calculations (DFT(SVWN)) were not reliable for locating transition state structures whereas the post-LDA ones (DFT(B88/P86)) led to the transition state structures and ener-... 

Figure 12.3 (a) The active site of human carbonic anhydrase and (b) a simplified mechanism of action for the enzyme B = general base, probably His64. (Reprinted with permission from Parkin, 2004. Copyright (2004) American Chemical Society.)... 

C. K. Tu, D. N. Silverman, C. Forsman, B. H. Jonsson, S. Lindskog, Role of Histidine 64 in the Catalytic Mechanism of Human Carbonic Anhydrase II Studied with a Site-Specific Mutant , Biochemistry 1989, 28, 7913-7918. 

A. E. Eriksson, T. A. Jones, A. Lilijas, Redefined Structure of Human Carbonic Anhydrase at A Resolution , Proteins Struct., Fund., Genet. 1988, 4, 274 - 282. 

The buried Cys-212 of human carbonic anhydrase B (3 pM) is virtually unreactive towards 2-chloromercuric-4-nitrophenol (60 pM) at pH 9.2, but upon the addition of only 40 pM CN , the half-life drops to 10 minutes which is an, at least, 75-fold rate enhancement. On first analysis, this would suggest that inhibitor binding to the enzyme has produced a conformational change or altered the — SH environment of the Cys—212. This is unexpected. How would you prove by kinetic experiments that the CN is binding to the mercury compound and not the enzyme and that this is changing the reactivity. The rate reaches a constant value at high [CN ]. 

Fig. 14. Paramagnetic enhancements to water NMRD profiles for solutions of cobalt(II) human carbonic anhydrase I at pH 9.9 and 298 K ( ) (48,49) and for solutions of the nitrate adduct of cobalt(II) bovine carbonic anhydrase II at pH 6.0 and 298 K ( ) (126). The dashed line shows the best fit profile of the former data calculated with including the effect of ZFS, whereas the dotted line shows the best fit profile calculated without including the effect of ZFS.

Rowlett and Silverman used a Brpnsted plot to examine the interaction of external buffers with human carbonic anhydrase II. The buffers act as proton acceptors in the removal of the proton generated by the enzyme-catalyzed reaction. The Brpnsted plot displays a plateau at a value of about 10 for the catalytic rate... 

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... 

X-Ray crystallographic studies of native human carbonic anhydrase II have been reported at 2.0 A resolution (Eriksson et al, 1986, 1988a). Important active-site residues include Thr-199, Thr-200, Glu-106, His-64, Trp-209, Val-121, Val-143, the zinc ion (liganded by His-94, His-96, and His-119), and the zinc-bound hydroxide ion. A schematic view of the active site is found in Fig. 22. The globular protein has a molecular... 

Fig. 26. Electron density map, calculated with Fourier coefficients 2 Fo - [fj and phases calculated from the final model, of the hydrophobic pocket of the Val-14S- Tyr mutant of human carbonic anhydrase II (Alexander etai, 1991). This mutation nearly obliterates the pocket and results in a 10 -fold loss of activity (Fierke et ai, 1991).

Orally administered carbonic anhydrase inhibitors lower the intraocular pressure of glaucoma patients, however they induce a number of intolerable side effects associated with extraocular inhibition of the enzyme [5,6]. Thus, much research has been directed towards the search for a topically effective agent. Several compounds have been synthesized since the 1980 s in Merck Sharp Dohme Research Laboratories, and have been found to be topically active in man [7]. Unfortunately, many of these compounds were not very soluble. Attempts to obtain an active carbonic anhydrase inhibitor with good solubility resulted in the synthesis of Dorzolamide hydrochloride [8,9], which was first made available for pharmacological evaluation in 1987. Like other carbonic anhydrase inhibitors sulfonamides (such as acetazolamide, ethoxzolaniide, and methazolamide) dorzolamide is an inhibitor of human carbonic anhydrase isoenzymes I, II, and IV. In contrast to the other sulfonamides, dorzolamide is a potent inhibitor of isoenzymes II and IV, and a weak inhibitor of isoenzyme I [ 10]. Isoenzyme II is thought to play a major role in aqueous humor secretion. 

Dorzolamide Hydrochloride is an inhibitor of human carbonic anhydrase II. The inhibition of carbonic anhydrase in the ciliary processes of the eye decreases the secretion of aqueous humor, with a resulting reduction in intraocular pressure. The drug is formulated as an ophthalmic solution, and administered topically as eyedrops. 

Indeed, Ellis s group provided some very nice examples of the application of Zn NMR spectroscopy when applied to proteins, such as the Minimal DNA Binding Domain of Human Nucleotide Excision Repair Protein XPA and the Human Carbonic Anhydrase. ... 

Two stable bicarbonato complexes of bis(l,10-phenanthroline) copper(II) were reported for the first time by Mao et al. (44). These are akin to the Lipscomb and Lindskog structures of human carbonic anhydrase (HCA) (45). In the Lipscomb structure the bicarbonate acts as a bidentate ligand while in the Lindskog structure it is essentially coordinated to the metal center in unidentate fashion (Fig. 2). 

There are several types of -class CAs i.e., a-CA I-VII, reported in the literature, out of which the human carbonic anhydrase II (HCA II), the most extensively studied carbonic anhydrase, has an exceptionally high CO2 hydration rate and a wide tissue distribution 107). The HCA II comprises a single polypeptide chain with a molecular mass of 29.3 kDa and contains one catalytic zinc ion, coordinated to three histidine residues, His 94, His 96, and His 119. A tetrahedral coordination geometry around the metal center is completed with a water molecule, which forms a hydroxide ion with a pK value of 7.0 108). Quigley and co-workers 109,110) reported that the inhibition of the synthesis of HCO3 from CO2 and OH- reduces aqueous humor formation and lowers intra-ocular pressure, which is a major risk factor for primary open-angle glaucoma. 

Applications to Biological Samples. - Methods of distance measurements were compared for four doubly spin-labelled derivatives of human carbonic anhydrase.53 The distances between the spin labels were obtained from continuous wave spectra by analysis of the relative intensity of the half-field transition, Fourier deconvolution of the line-shape broadening, and computer simulation of line-shape changes. For variants with interspin distances greater than 18 A, the DEER method also was used. For each variant, at least two methods were applicable and reasonable agreement between distances obtained by different methods was obtained. The useful distance ranges for the techniques employed at X-band with natural isotope abundance spin labels were estimated to be half-field transition (5-10 A), line-shape simulation (up to 15 A), Fourier deconvolution (8 - 20 A), and four-pulse DEER (> 18 A).53... 

Figure B3.1.3 An isoelectric focusing (IEF) gel, pH 3 to 10. Lane 1, 4 pg purified egg white cystatin. Lane M, broad-range pi standards trypsinogen (pi 9.3), lentil lectin-basic band (pi 8.65), lentil lectin-middle band (pi 8.45), lentil lectin-acidic band (pi 8.15), myoglobin-basic band (pi 7.35 visible as a broad band), myoglobin-acidic band (pi 6.85), human carbonic anhydrase B (pi 6.55), bovine carbonic anhydrase (pi 5.85), a-lactoglobulin A (pi 5.20), soybean trypsin inhibitor (pi 4.55), and amyloglucosidase (pi 3.50) in order shown from top of gel. The pi values of the two purified egg white cystatin isomers were determined to be 6.6 (upper band) and 5.8 (lower band). Adapted from Akpinar (1998) with permission from author.

The structure of the human carbonic anhydrase B-imidazole complex involves five-coordinate zinc, the aqua group being retained.486 This is an important result in view of the competitive inhibition by imidazole. Sulfonamides displace the aqua ligand, being bound to the zinc by an O or N donor atom, with a second O atom forming an additional long bond to the zinc, making it... 

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