Carbonic anhydrase activity and

A wide variety of sulfamate esters have been synthesised and screened as herbicides, pharmaceutical agents and sweeteners (see Chapter 11, p. 240). Sulfamates containing a primary amino group (124) are conveniently prepared by condensation of the appropriate alcohol with sulfamoyl chloride (125) in DMF in the presence of sodium hydride (Scheme 50). An illustrative example is provided by the conversion of substituted p-phenylethanols (126) to the corresponding sulfamates (127) (Scheme 50). Compounds of type (127) exhibit anticonvulsant and carbonic anhydrase activity and may be useful in the treatment of epilepsy and glaucoma. Sulfamoyl chlorides (125) may be prepared by treatment of amines or amine hydrochlorides with sulfuryl chloride (128). An analogous reaction also occurs with dialkyl sulfonamides (129) (Scheme 51). 

Muntwyler E, lacobellis M, Griffin GE. 1956. Kidney glutaminase and carbonic anhydrase activities and renal electrol5fe excretion in rats. Am J Physiol 184 83-90. 

Kirghgessner M, Stabler AE and Roth HP (1975) Carbonic anhydrase activity and erythrocyte count in the blood of zinc-d wient rats. Bioinor-ganic Chemistry 5 33—38. 

The data in Table 1 show that 18-7F, like wild type, induces the CO2 concentrating mechanism. Both external carbonic anhydrase activity and apparent photosynthetic affinity for CO2 increase dramatically in air-adapted cells. In spite of induction of the concentrating mechanism, 18-7F shows both oxygen and light inhibition of photosynthetic O2 evolution (Fig 1). 

HMG-CoA reductase, whilst in other situations the enzyme S5 tems are involved in a variety of functions, e.g. phosphodiesterases. The following sections detail aspects of lipid-lowering dmgs including the action of statins with HMG-CoA reductase, the suiphonamide diuretics and carbonic anhydrase activity and their involvement with the Na/Q/K symporter, ACE inhibitors, a number of different pbospbcxUesterase inbibitors involved in erertile dysfunction and cbronic obstructive pulmonary disease and tbe proton pump inbibitors used in tbe treatment of gastric ulcers. 

The X-ray structure of the unsubstituted tris(pyrazolyl)borato zinc nitrate has been solved showing a unidentate coordination mode for nitrate, in contrast with the t-butyl substituted ligand, which shows anisobidentate nitrate coordination due to the steric effects.232 A partial explanation of the reduced activity of cadmium-substituted carbonic anhydrase is offered by Parkin on the basis of the comparison of nitrate coordination to cadmium and zinc trispyrazo-lylborate moieties. A contributing factor may be the bidentate coordination supported by the cadmium that does not allow the facile access to a unidentate bicarbonate intermediate, which could be highly important to carbonic anhydrase activity.233... 

Segments of human aorta obtained fresh at autopsy were freed from blood and covering connective tissue and analyzed manometrically for carbonic anhydrase activity. Twelve specimens from 7 males and 5 females yielded nearly a 9-fold spread in values (0.12 to 1.05 units).31 This is interesting in view of the zinc content of carbonic anhydrase and the extremely wide variations in the zinc content of blood plasma and spleens which have been observed (pp. 55 and 72). 

The fact that zinc is known to be a component of an enzyme carbonic anhydrase leaves no doubt as to its physiological significance. The amount of zinc in erythrocytes seems to parallel the carbonic anhydrase activity.21 The leucocytes which appear to lack carbonic anhydrase contain about 25 times as much zinc (per cell) as do the erythrocytes.20 It seems likely that an investigation of the zinc content of different types of white blood cells coupled with a study of individuals from the standpoint of the different types of white cells present (p. 35) would lead to the discovery of substantial inter-individual differences. The wide spread in the zinc concentrations in three human spleens has already been mentioned (p. 72). A recent study has been made of the intake and excretion of zinc by 13... 

Drugs of this group inhibit activity of carbonic anhydrase, an enzyme that catalyzes the reversible reaction of water and carbon dioxide, which forms carbonic acid. The mechanism of action of this group of drags is not fuUy understood. However, inhibition of carbonic anhydrase activity leads to a reduction of carbonic acid formation and an increase in bicarbonate, sodium, and potassium excretion with urine, which eventually leads to a significant increase in the process of excreting water from the organism. 

Tempering C., Scozzafava, A., Puccetti, L., and Supuran, C. (2005). Carbonic anhydrase activators X-ray crystal structure of the adduct of human isozyme II with histidine as a platform for the design of stronger activators. Bioorg. Med. Chem. Lett. 15,5136-5141. 

Subsequent to CO2 association in the hydrophobic pocket, the chemistry of turnover requires the intimate participation of zinc. The role of zinc is to promote a water molecule as a potent nucleophile, and this is a role which the zinc of carbonic anhydrase II shares with the metal ion of the zinc proteases (discussed in the next section). In fact, the zinc of carbonic anhydrase II promotes the ionization of its bound water so that the active enzyme is in the zinc-hydroxide form (Coleman, 1967 Lindskog and Coleman, 1973 Silverman and Lindskog, 1988). Studies of small-molecule complexes yield effective models of the carbonic anhydrase active site which are catalytically active in zinc-hydroxide forms (Woolley, 1975). In addition to its role in promoting a nucleophilic water molecule, the zinc of carbonic anhydrase II is a classical electrophilic catalyst that is, it stabilizes the developing negative charge of the transition state and product bicarbonate anion. This role does not require the inner-sphere interaction of zinc with the substrate C=0 in a precatalytic complex. 

The thiazidelike compounds, including chlorthalidone Hygrown), quinethazone (Hydromox), and metolazone (Zaroxolyn) have similar mechanisms of action, but they differ substantially from one another in their duration of action, the degree of carbonic anhydrase inhibition, and the dose required for maximum natriuretic activity. 

The inhibition of CA II and total carbonic anhydrase activities was found below the degree of inhibition anticipated to be necessary for a pharmacological effect on renal function and respiration when dorzolamide was administered orally at 2 mg b.i.d for up to 20 weeks [14]. 

C. T. Supuran, D. Vullo, G. Manole, A. Casini, A. Scozzafava (2004). Designing of novel carbonic anhydrase inhibitors and activators. Curr. Med. Chem. Cardiovasc. Hematol. Agents 2 49-68. 

In maximal doses, chlorothiazide will markedly increase excretion of water, Na, K+, Cl and HCOj". Chlorothiazide due to its weak carbonic anhydrase activity, can cause some loss of bicarbonate in therapeutic dose. 

Other reports concerning chemically modified amino acid as metal chelating agents used for the carbonic anhydrase active site model reconstruction are in close agreement with the small contribution of Zn(II) binding to the proton chemical shift variation discussed above. NMR experiments carried out in DMSO-rfg, at 300 K, and the observed... 

Very recently the isolation of still active carbonic anhydrase from the biocrystalline layer of hens egg shells has been reported. Crude egg shell extracts exhibited no enzyme activity. however, after removal of Ca2+ and simple gel filtration of the extracts, carbonic anhydrase activity could be measured. Further purification steps led to the isolation of two isoenzymes. The possibility of inhibition of this enzyme activity by shell components cannot be excluded although recombination of shell components after separation did not inhibit that enzyme. The isolated enzymes has an apparent molecular size of 28,000 daltons. Carbonic anhydrase from egg shells catalyzes the reversible hydration of CO2 + HOH H+ + HCO3-. This probably is the primary action of the enzyme of the shell. Moreover, egg shell carbonic anhydrase catalyzes the hydration of acetaldehyde and pyridine aldehyde. Furthermore, the same enzymes have esterase activity (hydrolysis of p-nitrophenyl acetate). Whether the latter activities play a role in the egg shell cannot be judget at the present time. 

Carbonic anhydrase activities of the egg shells are inhibited by reaction with p-mercuribenzoate by blocking reactive SH-groups of the enzyme. Omission of 2-mercaptoethanol from buffer solutions for extraction and fractionation also resul-... 

There is general agreement that carbonic anhydrase activity is linked to the zinc ion and its ligands. At the active site water is bound to the zinc but the state and involvement of the water in the actual catalysis is a matter of controversy. According to a widely accepted opinion the zinc-bound water is ionized and the activity is a function of pH1S6. ... 

Deposition of mineral matter is limited by diffusion of calcium and/or phosphorus to the site of deposition400-. Since the transfer of both compounds is enzymatically controlled (see p. 21) equilibrium relationships may change environmental settings critical for the deposition of minerals. For instance, by limiting carbonic anhydrase activity in one direction, a pool of H2C03 may build up at the site of deposition in the reverse situation HC03 will concentrate. As a consequence,... 

It is likely that at low zinc concentrations there is impairment of the activity of vital zinc metalloenzymes such as lactic dehydrogenase, alkaline phosphatase, carbonic anhydrase, carboxypeptidase, and of enzymes in which zinc acts as a cofactor. Injection experiments showed that radioactive 65Zn preferentially concentrated in healing tissues27. ... 

Supuran, C.T. Carbonic anhydrases catalytic and inhibition mechanism, distribution and physiological roles. In Carbonic Anhydrase Its Inhibitors and Activators, ed. Supuran, C.T., Scozzafava, A., Conway, J., CRC Press Boca Raton, FL, 2004, pp. 1-24. 

Inhibition of carbonic anhydrase activity profoundly depresses bicarbonate reabsorption in the proximal tubule. At its maximal safely administered dosage, 85% of the bicarbonate reabsorptive capacity of the superficial proximal tubule is inhibited. Some bicarbonate can still be absorbed at other nephron sites by carbonic anhydrase-independent mechanisms, and the overall effect of maximal acetazolamide dosage is about 45% inhibition of whole kidney bicarbonate reabsorption. Nevertheless, carbonic anhydrase inhibition causes significant bicarbonate losses and hyperchloremic metabolic acidosis. Because of this and the fact that HCO3" depletion leads to enhanced NaCl reabsorption by the remainder of the nephron, the diuretic efficacy of acetazolamide decreases significantly with use over several days. 

Landolfi et al. (1997) reported a modified procedure for the measurement of carbonic anhydrase activity. The measure of carbonic anhydrase activity is based on the rate of CO2 hydration by the enzyme. Such transformation was monitored by a procedure which consists of the measure of time necessary for the pH of an appropriate buffer to decrease from 8 to 7.5 in the presence of a constant CO2 flow this time period is dose-dependently reduced by the addition of the enzyme and further modified in the presence of carbonic anhydrase inhibitory compounds. 

Landolfi C, Marchetti M, Ciocci G, Milanese C (1997) Development and pharmacological characterization of a modified procedure for the measurement of carbonic anhydrase activity. J Pharmacol Toxicol Meth 38 169-172 Maren TH (1960) A simplified micromethod for the determination of carbonic anhydrase and its inhibitors. J Pharmacol Exp Ther 130 26-29... 

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