A ternary complex of carbonic anhydrase: X-ray crystallographic structure of the adduct of human carbonic anhydrase II with the activator phenylalanine and the inhibitor azide

Insight into the activation mechanism of carbonic anhydrase(II) through 2-(2-aminoethyl)-pyridine: a promising pathway for enhanced enzymatic activity

Activation of human carbonic anhydrase II (hCA II) holds great promise for treating memory loss symptoms associated with Alzheimer's disease. Despite its importance, the activation mechanism of hCA II has been largely overlooked in favor of the well-studied inhibition mechanism. To address this unexplored realm, we use first-principles calculations to tease out the activation mechanism of hCA II using 2-(2-aminoethyl)-pyridine (2-2AEPy), a promising in vitro activator. We explored both stepwise and concerted mechanisms via both available nitrogen sites of 2-2AEPy: (i) aminoethyl group (Nα) and (ii) pyridine ring (Nβ). Our results show that a concerted mechanism via Nα holds the key to hCA II activation. The activation process of the concerted mechanism exhibits the characteristics of an exergonic reaction, wherein the transition state resembles the reactant with a notably low imaginary frequency of 452.4i cm-1 and barrier height of 5.2 kcal mol-1. Such meager transition barriers propel the activation of hCA II at in vivo temperatures. These findings initiate future research into hCA II activation mechanisms and the development of efficient activators, which may lead to promising therapeutic interventions for Alzheimer's disease.

Tracking solvent and protein movement during CO2 release in carbonic anhydrase II crystals

Carbonic anhydrases are mostly zinc metalloenzymes that catalyze the reversible hydration/dehydration of CO2/HCO3 (-) Previously, the X-ray crystal structures of CO2-bound holo (zinc-bound) and apo (zinc-free) human carbonic anhydrase IIs (hCA IIs) were captured at high resolution. Here, we present sequential timeframe structures of holo- [T = 0 s (CO2-bound), 50 s, 3 min, 10 min, 25 min, and 1 h] and apo-hCA IIs [T = 0 s, 50 s, 3 min, and 10 min] during the "slow" release of CO2 Two active site waters, WDW (deep water) and WDW' (this study), replace the vacated space created on CO2 release, and another water, WI (intermediate water), is seen to translocate to the proton wire position W1. In addition, on the rim of the active site pocket, a water W2' (this study), in close proximity to residue His64 and W2, gradually exits the active site, whereas His64 concurrently rotates from pointing away ("out") to pointing toward ("in") active site rotameric conformation. This study provides for the first time, to our knowledge, structural "snapshots" of hCA II intermediate states during the formation of the His64-mediated proton wire that is induced as CO2 is released. Comparison of the holo- and apo-hCA II structures shows that the solvent network rearrangements require the presence of the zinc ion.

Carbonic Anhydrase Activators. Activation of Isozymes I, II, IV, VA, VII, and XIV withL- andD-Histidine and Crystallographic Analysis of Their Adducts with Isoform II: Engineering Proton-Transfer Processes within the Active Site of an Enzyme

Activation of six human carbonic anhydrases (CA, EC 4.2.1.1), that is, hCA I, II, IV, VA, VII, and XIV, with l- and d-histidine was investigated through kinetics and by X-ray crystallography. l-His was a potent activator of isozymes I, VA, VII, and XIV, and a weaker activator of hCA II and IV. d-His showed good hCA I, VA, and VII activation properties, being a moderate activator of hCA XIV and a weak activator of hCA II and IV. The structures as determined by X-ray crystallography of the hCA II-l-His/d-His adducts showed the activators to be anchored at the entrance of the active site, contributing to extended networks of hydrogen bonds with amino acid residues/water molecules present in the cavity, explaining their different potency and interaction patterns with various isozymes. The residues involved in l-His recognition were His64, Asn67, Gln92, whereas three water molecules connected the activator to the zinc-bound hydroxide. Only the imidazole moiety of l-His interacted with these amino acids. For the d-His adduct, the residues involved in recognition of the activator were Trp5, His64, and Pro201, whereas two water molecules connected the zinc-bound water to the activator. Only the COOH and NH(2) moieties of d-His participated in hydrogen bonds with these residues. This is the first study showing different binding modes of stereoisomeric activators within the hCA II active site, with consequences for overall proton-transfer processes (rate-determining for the catalytic cycle). The study also points out differences of activation efficiency between various isozymes with structurally related activators, convenient for designing alternative proton-transfer pathways, useful both for a better understanding of the catalytic mechanism and for obtaining pharmacologically useful derivatives, for example, for the management of Alzheimer's disease.

Carbonic anhydrase activators: X-ray crystal structure of the adduct of human isozyme II with L-histidine as a platform for the design of stronger activators

Activation of the carbonic anhydrase (CA, EC 4.2.1.1) isoforms hCA I, II, and IV with l-histidine and some of its derivatives has been investigated by kinetic and X-ray crystallographic methods. l-His was a potent activator of isozymes I and IV (activation constants in the range of 4-33microM), and a moderate hCA II activator (activation constant of 113microM). Both carboxy- as well as amino-substituted l-His derivatives, such as the methyl ester or the dipeptide carnosine (beta-Ala-His), acted as more efficient activators as compared to l-His. The X-ray crystallographic structure of the hCA II-l-His adduct showed the activator to be anchored at the entrance of the active site cavity, participating in an extended network of hydrogen bonds with the amino acid residues His64, Asn67, and Gln92 and, with three water molecules connecting it to the zinc-bound water. Although the binding site of l-His is similar to that of histamine, the first CA activator for which the X-ray crystal structure has been reported in complex with hCA II (Briganti, F.; Mangani, S.; Orioli, P.; Scozzafava, A.; Vernaglione, G.; Supuran, C. T. Biochemistry1997, 36, 10384) there are important differences of binding between the two structurally related activators, since histamine interacts among others with Asn67 and Gln92 (similarly to l-His), but also with Asn62 and not His64, whereas the number of water molecules connecting them to the zinc-bound water is different (two for histamine, three for l-His). Furthermore, the imidazole moieties of the two activators adopt different conformations when bound to the enzyme active site. Since neither the amino- nor carboxy moieties of l-His participate in interactions with amino acid moieties of the active site, they can be derivatized for obtaining more potent activators, with pharmacological applications for the enhancement of synaptic efficacy. This may constitute a novel approach for the treatment of Alzheimer's disease, aging, and other conditions in need of achieving spatial learning and memory therapy.

Carbonic anhydrase inhibitors. Interaction of isozymes I, II, IV, V, and IX with organic phosphates and phosphonates

The interaction of five human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes, that is, hCA I, II, IV, V, and IX with a small library of phosphonic acids/organic phosphates, including methylphosphonic acid, MPA; phenylphosphonic acid, PPA; N-(phosphonoacetyl)-L-aspartic acid, PALA, methylene diphosphonic acid MDPA, the O-phosphates of serine (Ser-OP) and threonine (Thr-OP) as well as the antiviral phosphonate foscarnet has been studied. hCA I was activated by all these compounds, with the best activators being MPA and PPA (K(A)s of 0.10-1.20 microM). MPA and PPA were on the other hand nanomolar inhibitors of hCA II (K(I)s of 98-99 nM). PALA showed an affinity of 7.8 microM, whereas the other compounds were weak, millimolar inhibitors of this isozyme. The best hCA IV inhibitors were PALA (79 nM) and PPA (5.4 microM), whereas the other compounds showed K(I)s in the range of 0.31-5.34 mM. The mitochondrial isozyme was weakly inhibited by all these compounds (K(I)s in the range of 0.09-41.7 mM), similarly to the transmembrane, tumor-associated isozyme (K(I)s in the range of 0.86-2.25 mM). Thus, phosphonates may lead to CA inhibitors with selectivity against two physiologically relevant isozymes, the cytosolic hCA II or the membrane-bound hCA IV.

Carbonic anhydrase inhibitors. Interaction of isozymes I, II, IV, V, and IX with carboxylates

A detailed inhibition study of five carbonic anhydrase (CA, EC 4.2.1.1) isozymes with carboxylates including aliphatic (formate, acetate), dicarboxylic (oxalate, malonate), hydroxy/keto acids (l-lactate, l-malate, pyruvate), tricarboxylic (citrate), or aromatic (benzoate, tetrafluorobenzoate) representatives, some of which are important intermediates in the Krebs cycle, is presented. The cytosolic isozyme hCA I was strongly activated by acetate, oxalate, pyruvate, l-lactate, and citrate (K(A) around 0.1 microM), whereas formate, malonate, malate, and benzoate were weaker activators (K(A) in the range 0.1-1mM). The cytosolic isozyme hCA II was weakly inhibited by all the investigated anions, with inhibition constants in the range of 0.03-24 mM. The membrane-associated isozyme hCA IV was the most sensitive to inhibition by carboxylates, showing a K(I) of 99 nM for citrate and oxalate, of 2.8 microM for malonate and of 14.5 microM for pyruvate among others. The mitochondrial isozyme hCA V was weakly inhibited by all these carboxylates (K(I)s in the range of 1.67-25.9 mM), with the best inhibitor being citrate (K(I) of 1.67 mM), whereas this is the most resistant CA isozyme to pyruvate inhibition (K(I) of 5.5mM), which may be another proof that CA V is the isozyme involved in the transfer of acetyl groups from the mitochondrion to the cytosol for the provision of substrate(s) for de novo lipogenesis. Furthermore, the relative resistance of CA V to inhibition by pyruvate may be an evolutionary adaptation of this mitochondrial isozyme to the presence of high concentrations of this anion within this organelle. The transmembrane, tumor-associated isozyme hCA IX was similar to isozyme II in its slight inhibition by all these anions (K(I) in the range of 1.12-7.42 mM), except acetate, lactate, and benzoate, which showed a K(I)>150 mM. The lactate insensitivity of CA IX also represents an interesting finding, since it is presumed that this isozyme evolved in such a way as to show a high catalytic activity in hypoxic tumors rich in lactate, and suggests a possible metabolon in which CA IX participates together with the monocarboxylate/H(+) co-transporter in dealing with the high amounts of lactate/H(+) present in tumors.

Carbonic anhydrase inhibitors. Interaction of isozymes I, II, IV, V, and IX with phosphates, carbamoyl phosphate, and the phosphonate antiviral drug foscarnet

A detailed inhibition study of five carbonic anhydrase (CA, EC 4.2.1.1) isozymes with inorganic phosphates, carbamoyl phosphate, the antiviral phosphonate foscarnet as well as formate is reported. The cytosolic isozyme hCA I was weakly inhibited by neutral phosphate, strongly inhibited by carbamoyl phosphate (K(I) of 9.4 microM), and activated by hydrogen- and dihydrogenphosphate, foscarnet and formate (best activator foscarnet, K(A)=12 microM). The cytosolic isozyme hCA II was weakly inhibited by all the investigated anions, with carbamoyl phosphate showing a K(I) of 0.31 mM. The membrane-associated isozyme hCA IV was the most sensitive to inhibition by phosphates/phosphonates, showing a K(I) of 84 nM for PO(4)(3-), of 9.8 microM for HPO(4)(2-), and of 9.9 microM for carbamoyl phosphate. Foscarnet was the best inhibitor of this isozyme (K(I) of 0.82 mM) highly abundant in the kidneys, which may explain some of the renal side effects of the drug. The mitochondrial isozyme hCA V was weakly inhibited by all phosphates/phosphonates, except carbamoyl phosphate, which showed a K(I) of 8.5 microM. Thus, CA V cannot be the isozyme involved in the carbamoyl phosphate synthetase I biosynthetic reaction, as hypothesized earlier. Furthermore, the relative resistance of CA V to inhibition by inorganic phosphates suggests an evolutionary adaptation of this mitochondrial isozyme to the presence of high concentrations of such anions in these energy-converting organelles, where high amounts of ATP are produced by ATP synthetase, from ADP and inorganic phosphates. The transmembrane, tumor-associated isozyme hCA IX was on the other hand slightly inhibited by all these anions.

Effect of vitamin E on carbonic anhydrase enzyme activity in rainbow trout (Oncorhynchus mykiss) erythrocytes in vitro and in vivo

Considering that the excessive usage of vitamin E causes hypervitaminosis and thus reduces blood erythrocyte concentrations, therefore it is worth studying how its pharmacological dosage affects the activity of carbonic anhydrase (CA) enzyme found in erythrocytes of rainbow trout (Oncorhynchus mykiss) in vitro and in vivo. Vitamin E inhibited CA enzyme and the IC50 value of the vitamin was 0.039 mM in vitro. Similarly, it was seen that vitamin E inhibited CA enzyme activity after the first hour following vitamin E injections in vivo. The activities of CA in groups of trout given vitamin E injection were measured at 1, 3 and 5 h and the corresponding activities were found to be 772.7 +/- 290.5 (P < 0.05), 1286.4 +/- 378.2 and 1005.7 +/- 436.1 enzyme units (EU) g Hb(-1). The difference over the control was significant (P < 0.05) in the first hour and insignificant at 3 and 5 h (P > 0.05). The activity of CA in the control, which did not contain vitamin E, was determined as 1597.7 +/- 429.0 EU g Hb(-1).

Carbonic anhydrase inhibitors: the first selective, membrane-impermeant inhibitors targeting the tumor-associated isozyme IX

The inhibition of the tumor-associated transmembrane carbonic anhydrase IX (CA IX) isozyme possessing an extracellular active site has been investigated with a series of positively-charged, pyridinium derivatives of sulfanilamide, homosulfanilamide and 4-aminoethylbenzenesulfonamide. Inhibition data for the physiologically relevant isozymes I and II (cytosolic forms) and IV (membrane-bound) were also provided for comparison. A very interesting inhibition profile against CA IX with these sulfonamides has been observed. Several nanomolar (K(i)'s in the range of 6-54 nM) CA IX inhibitors have also been detected. Because CA IX is a highly active isozyme predominantly expressed in tumor tissues with bad prognosis of disease progression, this finding is very promising for the potential design of CA IX-specific inhibitors with applications as anti-tumor agents. This is the first report of inhibitors that may selectively target CA IX, due to their membrane-impermeability and high affinity for this clinically relevant isozyme.

Inhibitory effects of ammonia and urea on gill carbonic anhydrase enzyme activity of rainbow trout (Oncorhynchus mykiss)

The effects of ammonia and urea on branchial carbonic anhydrase (CA) enzyme which plays a key role in ionoregulation, osmoregulation and acid-base balance of rainbow trout (Oncorhynchus mykiss) were investigated. CA activity of the control group for ammonia and urea was determined as 1285.7 ± 67.9 and 1261.7 ± 60.8EU/mg protein, respectively. The CA enzyme activities of the other groups were measured at 1, 2 and 3h after ammonia and urea applications. The corresponding activities of ammonia were 774.9 ± 68.8, 732.1 ± 48.6 and 768.1 ± 59.5EU/mg protein, respectively and that of urea were 769.3 ± 58.9, 638.2 ± 47.7 and 1108.1 ± 61.1EU/mg protein, respectively. The differences between the initial CA activities for the controls was not significantly (P > 0.01). The CA activities were significantly (P < 0.01) inhibited both in ammonia and urea group. However, the ammonia inhibited more than urea since there was significant differences between final values of gill CA activities.

Carbonic anhydrase activators. The selective serotonin reuptake inhibitors fluoxetine, sertraline and citalopram are strong activators of isozymes I and II

The selective serotonin reuptake inhibitors (SSRI) fluoxetine, sertraline and citalopram have been investigated for their ability to activate two carbonic anhydrase (CA) isozymes, hCA I and hCA II, in parallel with two standard activators for which the X-ray structure (in complex with isozyme II) has been resolved: histamine and phenylalanine. All three SSRI activated both isozymes with potencies comparable to that of the standards although the profile was different: for hCA I, best activators were fluoxetine and histamine, with citalopram and sertraline showing weaker activity. For hCA II, the best activators were phenylalanine and citalopram, and the weakest histamine and sertraline, whereas fluoxetine showed an intermediate behavior. These results suggest that SSRI efficacy in major depression complicating Alzheimer's disease may be partly due to their ability to activate CA isozymes and may lead to the development of potent activators for the therapy of diseases associated with significant decreases in brain CA activity.

In vivo and in vitro effects of some plant hormones on rat erythrocyte carbonic anhydrase and glucose-6-phosphate dehydrogenase activities

The present study was undertaken to determine in vivo and in vitro effects of some plant growth regulators on rat erythrocyte carbonic anhydrase (CA) and glucose-6-phosphate dehydrogenase (G6PD) activities. Both in vivo and in vitro, spermidine and kinetin did not affect enzymatic activities of CA and G6PD, whereas putrescine decreased these activities, and abscisic acid increased them. Since plants use such growth regulators, their effects should be considered on mammals consuming them since they may possess important biological effects.

Carbonic anhydrase activators: human isozyme II is strongly activated by oligopeptides incorporating the carboxyterminal sequence of the bicarbonate anion exchanger AE1

Di-/tri- and especially tetrapeptides incorporating the sequence DADD present in the carboxyterminal region of the bicarbonate/chloride anion exchanger AE1 strongly activate human carbonic anhydrase (CA) isozyme II, whereas they act as more inefficient activators of isozymes I and IV. This discovery suggests that in the metabolon hCA II-AE1, the last protein plays a role both as a CA activator as well as a bicarbonate transporter. A synthesis of the tripeptide DAD and the tetrapeptide DADD is also presented together with the possible explanation why such highly acidic oligopeptides efficiently bind to hCA II but not to the closely related isozymes I and IV.

Carbonic anhydrase activators: synthesis of high affinity isozymes I, II and IV activators, derivatives of 4-(arylsulfonylureido-amino acyl)ethyl-1H-imidazole

Based on the X-ray crystallographic structure of the adduct of human carbonic anhydrase II (hCA II) with the weak activator histamine (Briganti, F., Mangani, S., Orioli, P., Scozzafava, A., Vernaglione, G. and Supuran, C.T. (1997) Biochemistry, 36, 10,384-10,392), a novel class of tight-binding CA activators was designed by using histamine (Hst) as lead molecule. Thus, N-1-tritylsulfenyl Hst was synthesized by reaction of Hst with tetrabromophthalic anhydride followed by protection of its imidazole moiety with tritylsulfenyl chloride. After hydrazinolysis, it afforded a key intermediate which was derivatized at the aliphatic amino group. Reaction of the key intermediate with 4-fluorophenylsulfonylureido amino acids (fpu-AA) or 2-toluenesulfonylureido amino acids (ots-AA) in the presence of carbodiimides, afforded after deprotection, a series of compounds with the general formula fpu/ots-AA-Hst (fpu = 4-FC6H4SO2NHCO; ots = 2-MeC6H4SO2NHCO). Some structurally related dipeptides with the general formula fpu/ots-AA1-AA2-Hst (AA, AA1 and AA2 represent amino acyl moieties), were also prepared, by a strategy similar to that used for the simple amino acyl compounds above. The new derivatives proved to be efficient in vitro activators of three CA isozymes. Best activity was shown against hCA I and bCA IV, for which some of the new compounds (such as the Lys, Arg, His or the dipeptide derivatives) showed affinities in the 2-12 nm range (h = human; b = bovine isozymes). hCA II was on the other hand somehow less prone to activation by the new derivatives, which possessed affinities around 30-60 nM for this isozyme. Ex vivo experiments showed some of the new activators to strongly enhance red cell CA activity (180-230%) after incubation with human erythrocytes. This new class of CA activators might lead to the development of drugs/diagnostic tools for the CA deficiency syndrome, a genetic disease of bone, brain and kidneys.

Carbonic anhydrase inhibitors - part 78(#). Synthesis of water-soluble sulfonamides incorporating beta-alanyl moieties, possessing long lasting-intraocular pressure lowering properties via the topical route

Reaction of 26 aromatic/heterocyclic sulfonamides containing amino, imino, hydrazino or hydroxyl groups with N-tert-butyloxycarbonyl-beta-alanine (Boc-beta-ala; Boc = t-butoxycarbonyl) in the presence of carbodiimide derivatives afforded, after removal of the protecting group, a series of water-soluble compounds (as salts of strong acids, such as hydrochloric, trifluoroacetic or trifluoromethane sulfonic). The new derivatives were assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA), and more precisely of three of its isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form), involved in important physiological processes. Good inhibition was observed against all three isozymes, but especially against CA II and CA IV (in the nanomolar range), the two isozymes known to play a critical role in aqueous humour secretion within the ciliary processes of the eye. Some of the best inhibitors synthesized were applied as 2% aqueous solutions into the eyes of normotensive or glaucomatous albino rabbits, when strong and long-lasting intraocular pressure (IOP) lowering was observed with many of them. Thus, the amino acyl groups conferring water solubility to these sulfonamide CA inhibitors, coupled with their strong enzyme inhibitory properties and balanced lipid solubility seem to be the key factors for obtaining compounds with effective topical antiglaucoma activity.

Carbonic anhydrase activators. Part 24. High affinity isozymes I, II and IV activators, derivatives of 4-(4-chlorophenylsulfonylureido-amino acyl)ethyl-1H-imidazole

N-1-Tritylsulfenyl histamine was synthesized by reaction of histamine (Hst) with tetrabromophthalic anhydride followed by protection of its imidazole moiety with tritylsulfenyl chloride. After hydrazinolysis, it afforded a key intermediate which was derivatized at the aminoethyl group in order to obtain new types of activators of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). Reaction of the key intermediate with 4-chlorophenylsulfonylureido amino acids (cpu-AA) in the presence of carbodiimides afforded, after deprotection of the imidazolic nitrogen atom, a series of compounds with the general formula cpu-AA-Hst (cpu, 4-ClC(6)H(4)SO(2)NHCO). Some structurally related dipeptide derivatives with the general formula cpu-AA1-AA2-Hst (AA, AA1 and AA2 represent amino acyl moieties) were also prepared by a strategy similar to that applied for the amino acyl compounds mentioned above. The new derivatives proved to be efficient activators of three CA isozymes. Best activity was detected against hCA I and bCA IV, for which some of the new compounds showed affinities in the 1-10 nM range (h, human; b, bovine isozymes). hCA II, on the other hand, was less prone to activation by the new derivatives, which possessed affinities around 20-50 nM for this isozyme. This new class of CA activators might lead to the development of drugs/diagnostic agents for CA deficiency syndrome, a genetic disease of bone, brain and kidneys.

Carbonic anhydrase activators: amino acyl/dipeptidyl histamine derivatives bind with high affinity to isozymes I, II and IV and act as efficient activators

Reaction of histamine (Hst) with tetrabromophthalic anhydride and protection of its imidazole moiety with tritylsulfenyl chloride, followed by hydrazinolysis, afforded N-1-tritylsulfenyl-histamine, a key intermediate which was further derivatized at its aminoethyl moiety. Reaction of the key intermediate with N-Boc-amino acids/dipeptides (Boc-AA) in the presence of carbodiimides afforded, after deprotection of the imidazolic and amino moieties, a series of compounds with the general formula AA-Hst (AA = amino acyl; dipeptidyl). The new derivatives were assayed as activators of three carbonic anhydrase (CA) isozymes, hCA I, hCA II (cytosolic forms) and bCA IV (membrane-bound form). Efficient activation was observed against all three isozymes, but especially against hCA I and bCA IV, with affinities in the nanomolar range for the best compounds. hCA II was, on the other hand, activatable with affinities around 10-20 nM. This new class of CA activators might lead to the development of drugs/diagnostic agents for the CA deficiency syndrome, a genetic disease of bone, brain and kidneys.

Carbonic anhydrase inhibitors. Part 79. Synthesis of topically acting sulfonamides incorporating GABA moieties in their molecule, with long-lasting intraocular pressure-lowering properties

Reaction of 26 aromatic/heterocyclic sulfonamides containing amino, imino, hydrazino or hydroxyl groups with N-tert-butoxycarbonyl-gamma-aminobutyric acid (Boc-GABA; Boc=t-butoxycarbonyl) in the presence of carbodiimide derivatives, afforded after removal of the protecting group, a series of water-soluble compounds (as salts of strong acids, such as hydrochloric, trifluoroacetic or trifluoromethane sulfonic). The new derivatives were assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA), and more precisely of three of its isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form), involved in important physiological processes. Some of the new compounds effectively inhibited CA II and CA IV (in the nanomolar range), the two isozymes known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the best inhibitors obtained as described above were applied as 2% water solutions into the eye of normotensive or glaucomatous albino rabbits, when strong and long-lasting intraocular pressure (IOP) lowering has been evidenced. Thus, the amino acyl tail conferring water solubility to these sulfonamides, coupled with their strong enzyme inhibitory properties and balanced lipid solubility seem to be the key factors for obtaining compounds with effective topical antiglaucoma activity from the class of the carbonic anhydrase inhibitors.

Novel carbonic anhydrase isozymes I, II and IV activators incorporating sulfonyl-histamino moieties

Sulfonylamido(ureido) derivatives of histamine were synthesized by an original procedure in order to obtain tight-binding activators of the zinc enzyme carbonic anhydrase (CA), exploiting the binding energy of the alkyl/arylsulfonyl moieties with amino acid residues at the entrance of the active site. In contrast to the lead molecule, histamine, the new derivatives possessed higher affinity for three different CA isozymes, as evidenced by compairing the affinity constants of these compounds for isozyme CA II.