Carbonic anhydrase activators: activation of the human isoforms VII (cytosolic) and XIV (transmembrane) with amino acids and amines

Enhanced Recognition Memory through Dual Modulation of Brain Carbonic Anhydrases and Cholinesterases

This study introduces a novel multitargeting strategy that combines carbonic anhydrase (CA) activators and cholinesterase (ChE) inhibitors to enhance cognitive functions. A series of tacrine-based derivatives with amine/amino acid moieties were synthesized and evaluated for their dual activity on brain CA isoforms and ChEs (AChE and BChE). Several derivatives, notably compounds 26, 30, 34, and 40, demonstrated potent CA activation, particularly of hCA II and VII, and strong ChE inhibition with subnanomolar to low nanomolar IC50 values. In vivo studies using a mouse model of social recognition memory showed that these derivatives significantly improved memory consolidation at doses 10-100 times lower than the reference compounds (either alone or in combination). Molecular modeling and ADMET predictions elucidated the compound binding modes and confirmed favorable pharmacokinetic and safety profiles. The findings suggest that dual modulation of CA and ChE activities is a promising strategy for treating cognitive deficits associated with neurodegenerative and psychiatric disorders.

New Histamine-Related Five-Membered N-Heterocycle Derivatives as Carbonic Anhydrase I Activators

A series of histamine (HST)-related compounds were synthesized and tested for their activating properties on five physiologically relevant human Carbonic Anhydrase (hCA) isoforms (I, II, Va, VII and XIII). The imidazole ring of HST was replaced with different 5-membered heterocycles and the length of the aliphatic chain was varied. For the most interesting compounds some modifications on the terminal amino group were also performed. The most sensitive isoform to activation was hCA I (K_A values in the low micromolar range), but surprisingly none of the new compounds displayed activity on hCA II. Some derivatives (1, 3a and 22) displayed an interesting selectivity for activating hCA I over hCA II, Va, VII and XIII.

Activation of carbonic anhydrase isoforms involved in modulation of emotional memory and cognitive disorders with histamine agonists, antagonists and derivatives

Carbonic anhydrases (CAs, EC 4.2.1.1) activators were shown to be involved in memory enhancement and learning in animal models of cognition. Here we investigated the CA activating effects of a large series of histamine based compounds, including histamine receptors (H1R - H4R) agonists, antagonists and other derivatives of this autacoid. CA activators may be thus useful for improving cognition as well as in diverse therapeutic areas (phobias, obsessive-compulsive disorder, generalised anxiety, post-traumatic stress disorders), for which activation of this enzyme was recently shown to be involved.

Effect of amino acids and amines on the activity of the recombinant ι-carbonic anhydrase from the Gram-negative bacterium Burkholderia territorii

We here report a study on the activation of the ι-class bacterial CA from Burkholderia territorii (BteCAι). This protein was recently characterised as a zinc-dependent enzyme that shows a significant catalytic activity (kcat 3.0 × 105 s-1) for the physiological reaction of CO2 hydration to bicarbonate and protons. Some amino acids and amines, among which some proteinogenic derivatives as well as histamine, dopamine and serotonin, showed efficient activating properties towards BteCAι, with activation constants in the range 3.9-13.3 µM. L-Phe, L-Asn, L-Glu, and some pyridyl-alkylamines, showed a weaker activating effect towards BteCAι, with KA values ranging between 18.4 µM and 45.6 µM. Nowadays, no information is available on active site architecture, metal ion coordination and catalytic mechanism of members of the ι-group of CAs, and this study represents another contribution towards a better understanding of this still uncharacterised class of enzymes.

Reconsidering anion inhibitors in the general context of drug design studies of modulators of activity of the classical enzyme carbonic anhydrase

Inorganic anions inhibit the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) generally by coordinating to the active site metal ion. Cyanate was reported as a non-coordinating CA inhibitor but those erroneous results were subsequently corrected by another group. We review the anion CA inhibitors (CAIs) in the more general context of drug design studies and the discovery of a large number of inhibitor classes and inhibition mechanisms, including zinc binders (sulphonamides and isosteres, dithiocabamates and isosteres, thiols, selenols, benzoxaboroles, ninhydrins, etc.); inhibitors anchoring to the zinc-coordinated water molecule (phenols, polyamines, sulfocoumarins, thioxocoumarins, catechols); CAIs occluding the entrance to the active site (coumarins and derivatives, lacosamide), as well as compounds that bind outside the active site. All these new chemotypes integrated with a general procedure for obtaining isoform-selective compounds (the tail approach) has resulted, through the guidance of rigorous X-ray crystallography experiments, in the development of highly selective CAIs for all human CA isoforms with many pharmacological applications.

Activation of carbonic anhydrases from human brain by amino alcohol oxime ethers: towards human carbonic anhydrase VII selective activators

The synthesis and carbonic anhydrase (CA; EC 4.2.1.1) activating effects of a series of oxime ether-based amino alcohols towards four human (h) CA isoforms expressed in human brain, hCA I, II, IV and VII, are described. Most investigated amino alcohol derivatives induced a consistent activation of the tested CAs, with K_As spanning from a low micromolar to a medium nanomolar range. Specifically, hCA II and VII, putative main CA targets when central nervous system (CNS) diseases are concerned, were most efficiently activated by these oxime ether derivatives. Furthermore, a multitude of selective hCA VII activators were identified. As hCA VII is one of the key isoforms involved in brain metabolism and other brain functions, the identified potent and selective hCA VII activators may be considered of interest for investigations of various therapeutic applications or as lead compounds in search of even more potent and selective CA activators.

Activation studies of the β-carbonic anhydrases from Malassezia restricta with amines and amino acids

The β-carbonic anhydrase (CA, EC 4.2.1.1) from the genome of the opportunistic pathogen Malassezia restricta (MreCA), which was recently cloned and characterised, herein has been investigated for enzymatic activation by a panel of amines and amino acids. Of the 24 compounds tested in this study, the most effective MreCA activators were L-adrenaline (KA of 15 nM), 2-aminoethyl-piperazine/morpholine (KAs of 0.25-0.33 µM), histamine, L-4-amino-phenylalanine, D-Phe, L-/D-DOPA, and L-/D-Trp (KAs of 0.32 - 0.90 µM). The least effective activators were L-/D-Tyr, L-Asp, L-/D-Glu, and L-His, with activation constants ranging between 4.04 and 12.8 µM. As MreCA is involved in dandruff and seborrhoeic dermatitis, these results are of interest to identify modulators of the activity of enzymes involved in the metabolic processes of such fungi.

Activation studies of the β-carbonic anhydrases from Escherichia coli with amino acids and amines

A β-carbonic anhydrase (CA, EC 4.2.1.1) from the widespread bacterium Escherichia coli (EcoCAβ), encoded by the CynT2 gene, has been investigated for its catalytic properties and enzymatic activation by a panel of amino acids and amines. EcoCAβ showed a significant catalytic activity for the hydration of CO2 to bicarbonate and a proton, with a kinetic constant kcat of 5.3 × 105 s- and a Michaelis-Menten constant KM of 12.9 mM. The most effective EcoCAβ activators were L- and D-DOPA, L-Tyr, 4-amino-Phe, serotonin and L-adrenaline, with KAs from 2.76 to 10.7 µM. L-His, 2-pyridyl-methylamine, L-Asn and L-Gln were relatively weak activators (KAs from 36.0 to 49.5 µM). D-His, L- and D-Phe, L- and D-Trp, D-Tyr, histamine, dopamine, 2-(aminoethyl)pyridine/piperazine/morpholine, L-Asp, L- and D-Glu have KAs from 11.3 to 23.7 µM. Endogenous CA activators may play a role in bacterial virulence and colonisation of the host.

Activation of α-, β-, γ- δ-, ζ- and η- class of carbonic anhydrases with amines and amino acids: a review

Eight genetically distinct carbonic anhydrase (EC 4.2.1.1) enzyme families (α-, β-, γ- δ-, ζ-, η-, θ- and ι-CAs) were described to date. On the other hand, 16 mammalian α-CA isoforms are known to be involved in many diseases such as glaucoma, edema, epilepsy, obesity, hypoxic tumors, neuropathic pain, arthritis, neurodegeneration, etc. Although CA inhibitors were investigated for the management of a variety of such disorders, the activators just started to be investigated in detail for their in vivo effects. This review summarizes the activation profiles of α-, β, γ-, δ-, ζ- and η- CAs from various organisms (animals, fungi, protozoan, bacteria and archaea) with the most investigated classes of activators, the amines and the amino acids.

The first activation study of the β-carbonic anhydrases from the pathogenic bacteria Brucella suis and Francisella tularensis with amines and amino acids

The activation of the β-class carbonic anhydrases (CAs, EC 4.2.1.1) from the bacteria Brucella suis and Francisella tularensis with amine and amino acids was investigated. BsuCA 1 was sensitive to activation with amino acids and amines, whereas FtuCA was not. The most effective BsuCA 1 activators were L-adrenaline and D-Tyr (K_As of 0.70–0.95 µM). L-His, L-/D-Phe, L-/D-DOPA, L-Trp, L-Tyr, 4-amino-L-Phe, dopamine, 2-pyridyl-methylamine, D-Glu and L-Gln showed activation constants in the range of 0.70–3.21 µM. FtuCA was sensitive to activation with L-Glu (K_A of 9.13 µM). Most of the investigated compounds showed a weak activating effect against FtuCA (K_As of 30.5–78.3 µM). Many of the investigated amino acid and amines are present in high concentrations in many tissues in vertebrates, and their role in the pathogenicity of the two bacteria is poorly understood. Our study may bring insights in processes connected with invasion and pathogenic effects of intracellular bacteria.

Investigation of piperazines as human carbonic anhydrase I, II, IV and VII activators

Four human (h) carbonic anhydrase isoforms (CA, EC 4.2.1.1), hCA I, II, IV, and VII, were investigated for their activation profile with piperazines belonging to various classes, such as N-aryl-, N-alkyl-, N-acyl-piperazines as well as 2,4-disubstituted derivatives. As the activation mechanism involves participation of the activator in the proton shuttling between the zinc-coordinated water molecule and the external milieu, these derivatives possessing diverse basicity and different scaffolds were appropriate for being investigated as CA activators (CAAs). Most of these derivatives showed CA activating properties against hCA I, II, and VII (cytosolic isoforms) but were devoid of activity against the membrane-associated hCA IV. For hCA I, the KAs were in the range of 32.6-131 µM; for hCA II of 16.2-116 µM, and for hCA VII of 17.1-131 µM. The structure-activity relationship was intricate and not easy to rationalize, but the most effective activators were 1-(2-piperidinyl)-piperazine (KA of 16.2 µM for hCA II), 2-benzyl-piperazine (KA of 17.1 µM for hCA VII), and 1-(3-benzylpiperazin-1-yl)propan-1-one (KA of 32.6 µM for hCA I). As CAAs may have interesting pharmacologic applications in cognition and for artificial tissue engineering, investigation of new classes of activators may be crucial for this relatively new research field.

The first activation studies of the η-carbonic anhydrase from the malaria parasite Plasmodium falciparum with amines and amino acids

The first activation study of a η-class carbonic anhydrase (CAs, EC 4.2.1.1) is reported. A panel of 24 natural and non-natural amino acids and amines was used to explore the activation profile of Plasmodium falciparum CA (PfACA). The most effective activators belonged to the amino acid chemotype, with d-Glu, l-Asp, l-/d-Phe and l-/d-DOPA possessing activation constant in the range of 82 nM-0.75 µM, whereas l-/d-His, l-Tyr, 4-amino-l-Phe and l-Gln were slightly less effective (K_A in the range of 1.00-2.51 µM. The only amine with submicromolar activating properties was 1-(2-aminoethyl-piperazine) with a K_A of 0.71 µM, whereas histamine, dopamine and serotonin showed K_A ranging between 7.18 and 9.97 µM. As CA activators have scarcely been investigated for their interaction with protozoan CAs, this study may be relevant for an improved understanding of the role of this enzyme in the life cycle of the malaria producing organisms belonging to the genus Plasmodium.

The first activation study of a δ-carbonic anhydrase: TweCAδ from the diatom Thalassiosira weissflogii is effectively activated by amines and amino acids

The activation of the δ-class carbonic anhydrase (CAs, EC 4.2.1.1) from the diatom Thalassiosira weissflogii (TweCAδ) was investigated using a panel of natural and non-natural amino acids and amines. The most effective activator of TweCAδ was d-Tyr (K_A of 51 nM), whereas several other amino acids and amines, such as L-His, L-Trp, d-Trp, dopamine and serotonin were submicromolar activators (K_As from 0.51 to 0.93 µM). The most ineffective activator of TweCAδ was 4-amino-l-Phe (18.9 µM), whereas d-His, l-/d-Phe, l-/d-DOPA, l-Tyr, histamine, some pyridyl-alkylamines, l-adrenaline and aminoethyl-piperazine/morpholine were moderately potent activators (K_As from 1.34 to 8.16 µM). For any δ-CA, there are no data on the crystal structure, homology modelling and the amino acid residues that are responsible for proton transfer to the active site are currently unknown making it challenging to provide a detailed rational for these findings. However, these data provide further evidence that this class of underexplored CA deserves more attention.

Activation studies with amines and amino acids of the β-carbonic anhydrase from the pathogenic protozoan Leishmania donovani chagasi

The activation of a β-class carbonic anhydrase (CAs, EC 4.2.1.1) from Leishmania donovani chagasi (LdcCA) was investigated using a panel of natural and non-natural amino acids and amines. The most effective activators belonged to the amine class, with histamine, dopamine, serotonin, 2-pyridyl-methylamine and 4-(2-aminoethyl)-morpholine with activation constants in the range of 0.23-0.94 µM. In addition, 2-(2-aminoethyl)pyridine and 1-(aminoethyl)-piperazine were even more effective activators (K_As of 9-12 nM). Amino acids such as L-/D-His, L-/D-Phe, L-/D-DOPA, L-/D-Trp and L-/D-Tyr were slightly less effective activators compared to the amines, but showed activation constants in the low micromolar range (1.27-9.16 µM). Many of the investigated activators are autacoids that are present in rather high concentrations in different tissues of the host mammals infected by these parasites. As CA activators have not yet been investigated for protozoan CAs, this study may be relevant for an improved understanding of the role of this enzyme in the life cycle of Leishmania.

Carbonic anhydrase activators

Mammalian carbonic anhydrases (CAs; EC 4.2.1.1) of which 16 isoforms are known, are involved in important physiological functions. Their inhibition is exploited pharmacologically for the treatment of many diseases (glaucoma, edema, epilepsy, obesity, hypoxic tumors, neuropathic pain, etc.) but the activators were less investigated till recently. A review on the CA activation is presented, with the activation mechanism, drug design approaches of activators and comparison of the various isoforms activation profiles being discussed. Some CAs, which are abundant in the brain, were recently demonstrated to be activatable by drug-like compounds, affording the possibility to design agents that enhance cognition, with potential therapeutic applications in aging and neurodegenerative diseases as well as tissue engineering.

Five- and Six-Membered Nitrogen-Containing Compounds as Selective Carbonic Anhydrase Activators

It has been proven that specific isoforms of human carbonic anhydrase (hCA) are able to fine-tune physiological pathways connected to signal processing, and that decreased CAs expression negatively influences cognition, leading to mental retardation, Alzheimer's disease, and aging-related cognitive dysfunctions. For this reason, a small library of natural and synthetic nitrogen containing cyclic derivatives was assayed as activators of four human isoforms of carbonic anhydrase (hCA I, II, IV and VII). Most of the compounds activated hCA I, IV and VII in the micromolar range, with K_As ranging between 3.46 and 80.5 μM, whereas they were not active towards hCA II (K_As > 100 μM). Two natural compounds, namely l-(+)-ergothioneine (1) and melatonin (2), displayed K_As towards hCA VII in the nanomolar range after evaluation by a CO₂ hydration method in vitro, showing a rather efficient and selective activation profile with respect to histamine, used as a reference compound. Corroborated with the above in vitro findings, a molecular modelling in silico approach has been performed to correlate these biological data, and to elucidate the binding interaction of these activators within the enzyme active site.

Burkholderia pseudomallei γ-carbonic anhydrase is strongly activated by amino acids and amines

Activation of the γ-class carbonic anhydrase (CAs, EC 4.2.1.1) from the pathogenic bacterium Burkholderia pseudomallei (BpsγCA) with a series of natural and non-natural amino acids and aromatic/heterocyclic amines has been investigated. The best BpsγCA activators were d-His, l-DOPA, d-Trp, 4-amino-l-Phe, dopamine, 2-(2-aminoethyl)pyridine, 2-aminoethyl-piparazine/morpholine and l-adrenaline, which showed activation constants ranging between 9 and 86nM. The least effective activators were l-His, l-Phe and 2-pyridyl-methylamine, with K_As in the range of 1.73-24.7μM. As little is known about the role of γ-CAs in the lifecycle and virulence of this saprophytic bacterium, this study may shed some light on such phenomena. This is the first CA activation study of a γ-CA from a pathogenic bacterium, the only other such study being on the enzyme discovered in the archaeon Methanosarcina thermophila, Cam.

Carbonic anhydrase activators: Activation of the β-carbonic anhydrase from Malassezia globosa with amines and amino acids

The β-carbonic anhydrase (CA, EC 4.2.1.1) from the dandruff producing fungus Malassezia globosa, MgCA, was investigated for its activation with amines and amino acids. MgCA was weakly activated by amino acids such as L-/D-His, L-Phe, D-DOPA, D-Trp, L-/D-Tyr and by the amine serotonin (KAs of 12.5-29.3μM) but more effectively activated by d-Phe, l-DOPA, l-Trp, histamine, dopamine, pyridyl-alkylamines, and 4-(2-aminoethyl)-morpholine, with KAs of 5.82-10.9μM. The best activators were l-adrenaline and 1-(2-aminoethyl)piperazine, with activation constants of 0.72-0.81μM. This study may help a better understanding of the activation mechanisms of β-CAs from pathogenic fungi as well as the design of tighter binding ligands for this enzyme which is a drug target for novel types of anti-dandruff agents.

Carbonic anhydrase activators: gold nanoparticles coated with derivatized histamine, histidine, and carnosine show enhanced activatory effects on several mammalian isoforms

Lipoic acid moieties were attached to amine or amino acids showing activating properties against the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). The obtained lipoic acid conjugates of histamine, L-histidine methyl ester, and L-carnosine methyl ester were attached to gold nanoparticles (NPs) by reaction with Au(III) salts in reducing conditions. The CA activators (CAAs)-coated NPs showed low nanomolar activation (K(A)s of 1-9 nM) of relevant cytosolic, membrane-bound, mitochondrial, and transmembrane CA isoforms, such as CA I, II, IV, VA, VII, and XIV. These NPs also effectively activated CAs ex vivo, in whole blood experiments, with an increase of 200-280% of the CA activity. This is the first example of enzyme activation with nanoparticles and may lead to biomedical applications for conditions in which the CA activity is diminished, such as aging, Alzheimer's disease, or CA deficiency syndrome.

An inhibitor-like binding mode of a carbonic anhydrase activator within the active site of isoform II

The 2,4,6-trimethylpyridinium derivative of histamine is an effective activator of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). However, unlike other CA activators, which bind at the entrance of the active site cavity, an X-ray crystal structure of hCA II in complex with the 1-[2-(1H-imidazol-4-yl)-ethyl]-2,4,6-trimethylpyridinium salt evidenced a binding mode never observed before either for activators or inhibitors of this enzyme, with the 2,4,6-trimethylpyridinium ring pointing towards the metal ion deep within the enzyme cavity, and several strong hydrophobic interactions stabilizing the adduct. Indeed, incubation of the activator with the enzyme for several days leads to potent inhibitory effects. This is the first example of a CA activator which after a longer contact with the enzyme behaves as an inhibitor.

Timolol activates the enzyme activities of human carbonic anhydrase I and II

Timolol, a beta-blocker, has been shown to be an effective ocular hypotensive agent when used alone or with carbonic anhydrase inhibitor on ocular hypertensive or open angle glaucoma patients. The effect of timolol hemihydrate on the CO(2) hydration activities of human carbonic anhydrase (HCA) I and II and their reaction mechanisms were investigated. Timolol activates the enzyme activities of HCA I and HCA II. In HCA I and II, the enzyme kinetic results clearly showed that timolol increases the value of V(max) but does not influence the value of K(m). The enzyme kinetic method showed that timolol noncompetitively activates HCA I and II activities through the formation of a ternary complex consisting of the enzyme, the substrate, and timolol. These results indicate that timolol binds apart from the narrow cavity of the active site. AutoDocking results showed that timolol binds at the entrance of the active site cavity in a region where the proton shuttle residue, His 64, of HCA I or II, is placed. The enzyme kinetic and AutoDocking results showed that timolol might weakly bind near the proton shuttle residue, His 64, to accelerate the proton transfer rate from His 64 to the buffer components. It is known that efficient activators of carbonic anhydrase possess a bulky aromatic/heterocyclic moiety and a primary/secondary amino group in their molecular structure. Timolol has a heterocyclic moiety and a secondary amino group, which are typical structures in efficient activators of carbonic anhydrase.

Carbonic anhydrase activators: activation of the beta-carbonic anhydrases from the pathogenic fungi Candida albicans and Cryptococcus neoformans with amines and amino acids

The proteins encoded by the Nce103 genes of Candida albicans and Cryptococcus neoformans are catalytically active beta-carbonic anhydrases (CAs, EC 4.2.1.1) playing various roles in the life cycle of these fungal pathogens, such as CO(2) sensing, regulation of capsule biosynthesis, filamentation, and adaptation of the organism to various pH and CO(2) conditions in various niches where the fungi grow. Here, we report the first activation study of these two enzymes, CaNce103 and Can2, respectively, with amines and amino acids. The C. albicans enzyme, CaNce103 was activated by amino acids such as L-/D-His, L-D-Trp, L-Tyr with K(A)s in the range of 19.5-46 microM. More effective activators were some amines such as histamine, dopamine, 2-aminoethyl-piperazine, and L-adrenaline (K(A)s of 13.2-18.5 microM). The best CaNce103 activators were L- and D-Dopa, with K(A)s of 0.96-2.5 microM. The C. neoformans enzyme, Can2, showed much lower propensity to be activated by all these amino acids and amines, which had activation constants in the range of 28.7-47.2 microM. The best Can2 activator was L-Trp. This study may help to better understand the catalytic/activation mechanisms of the beta-CAs and eventually to design CA activity modulators of such widespread enzymes in pathogenic fungi.

Carbonic anhydrase activators. Activation of the membrane-associated isoform XV with amino acids and amines

An activation study of the membrane-associated carbonic anhydrase (CA, EC 4.2.1.1) isoform XV with a series of natural and non-natural amino acids and aromatic/heterocyclic amines is reported. Murine CA XV was strongly activated by some amino acids (d-Phe, l-/d-DOPA, d-Trp, l-Tyr) and amines (dopamine, serotonin, l-adrenaline and 4-(2-aminoethyl)-morpholine) with activation constants in the range of 4.0-9.5muM. l-/d-His, l-Phe, histamine and several other heterocyclic amines showed less efficient activation (K(A)s in the range of 11.6-33.4muM). The activation profile of CA XV is quite different from that of the cytosolic isoforms CA I and II or the membrane-associated CA IV. All mammalian isoforms CA I-XV are thus characterized for their interaction with this set of amino acid and amine activators, some of which are biogenic amines or neurotransmitters present in sufficiently high amounts in various tissues for exerting significant biologic responses.

Carbonic anhydrase activators: activation of human isozymes I, II and IX with phenylsulfonylhydrazido l-histidine derivatives

Activation of the human carbonic anhydrase (CA, EC 4.2.1.1) isozymes I, II (cytosolic) and IX (transmembrane, tumor-associated isoform) with a series of arylsulfonylhydrazido-l-histidines incorporating 4-substituted-phenyl, pentafluorophenyl- and beta-naphthyl moieties was investigated. The compounds showed a weak hCA I activation profile, but were more efficient as hCA II and IX activators. The 4-iodophenyl-substituted derivative behaved as a strong and isozyme selective hCA II activator, with an activation constant of 0.21muM. This is the first isoform-selective, potent CA activator reported to date.

Carbonic anhydrase activators: activation of the beta-carbonic anhydrase Nce103 from the yeast Saccharomyces cerevisiae with amines and amino acids

The protein encoded by the Nce103 gene of Saccharomyces cerevisiae, a beta-carbonic anhydrase (CA, EC 4.2.1.1) designated as scCA, was investigated for its activation with amines and amino acids. scCA was poorly activated by amino acids such as l-/d-His, Phe, DOPA, Trp (K(A)s of 82-90 microM) and more effectively activated by amines such as histamine, dopamine, serotonin, pyridyl-alkylamines, aminoethyl-piperazine/morpholine (K(A)s of 10.2-21.3 microM). The best activator was l-adrenaline, with an activation constant of 0.95 microM. This study may help to better understand the catalytic/activation mechanisms of the beta-CAs and eventually to design modulators of CA activity for similar enzymes present in pathogenic fungi, such as Candida albicans and Cryptococcus neoformans.

Carbonic anhydrase activators: kinetic and X-ray crystallographic study for the interaction of D- and L-tryptophan with the mammalian isoforms I-XIV

An activation study of mammalian carbonic anhydrase (CA, EC 4.2.1.1) isoforms I-XIV with D- and L-tryptophan has been performed both by means of kinetic and X-ray crystallographic techniques. These compounds show a time dependent activity against isozyme CA II, with activation constants of 1.13 microM for L-Trp and 0.37 microM for D-Trp, respectively, after 24 h of incubation between enzyme and activator. The high resolution X-ray crystal structure of the hCA II-D-Trp adduct revealed the activator to bind in a totally unprecedented way to the enzyme active site as compared to histamine, L-/D-Phe, L-/D-His or L-adrenaline. D-Trp is anchored at the edge of the CA II active site entrance, strongly interacting with amino acid residues Asp130, Phe131 and Gly132 as well as with a loop of a second symmetry related protein molecule from the asymmetric unit, by means of hydrogen bonds and several weak van der Waals interactions involving Glu234, Gly235, Glu236 and Glu238. Thus, a second activator binding site (B) within the CA II cavity has been detected, where only D-Trp was shown so far to bind, in addition to the activator binding site A, in which histamine, L-/D-Phe, and L-/D-His are bound. These findings explain the strong affinity of D-Trp for CA II and may be useful for designing novel classes of CA activators by using this compound as lead molecule.

The mechanisms by which latanoprost free acid inhibits human carbonic anhydrase I and II

Latanoprost, a prostaglandin F2 alpha analogue, has been shown to be an effective ocular hypotensive agent when used alone on ocular hypertensive or open angle glaucoma patients. Carbonic anhydrase (CA) inhibitors are also used to reduce ocular hypertension by decreasing aqueous humor secretion, and are given in combination with prostaglandin F2 alpha analogue. It has been shown that prostaglandin F2 alpha, Minprostin F2 alpha, has been shown to increase the carbonic anhydrase (CA) activity and blood pressure. However, the effects of latanoprost on CA have not been clarified. Therefore, we studied the effects of latanoprost free acid on human carbonic anhydrase (HCA) I and II using the stopped flow method. Latanoprost free acid inhibited the hydration activity of HCA I or II by a noncompetitive mechanism. The inhibition constants (Ki) of latanoprost free acid for HCA I and II were 0.22 and 2.3 mM, respectively. Therefore, latanoprost free acid is a weak inhibitor of HCA I or II. AutoDock simulation of the latanoprost free acid-HCA I or II complex showed that the carboxylic moiety of latanoprost free acid, which is located at the end of the molecule, binds to the zinc ion of the active site by stretching of the chain of latanoprost free acid through the narrow and deep active site cavity of HCA I or II. In the active site cavity of HCA I or II, one side is hydrophilic and the other is hydrophobic. AutoDock simulation results clearly showed that latanoprost free acids lie down on the hydrophobic sides of the active site cavities in HCA I and II. The noncompetitive inhibition mechanism and the binding mode of latanoprost free acid indicate that the behavior of latanoprost free acid is very similar to that of simple anions.