Dual effects of aliphatic carboxylic acids on cresolase and catecholase reactions of mushroom tyrosinase

Catecholase and cresolase activities of mushroom tyrosinase (MT) were studied in presence of some n-alkyl carboxylic acid derivatives. Catecholase activity of MT achieved its optimal activity in presence of 1.0, 1.25, 2.0, 2.2 and 3.2?mM of pyruvic acid, acrylic acid, propanoic acid, 2-oxo-butanoic acid, and 2-oxo-octanoic acid, respectively. Contrarily, the cresolase activity of MT was inhibited by all type of the above acids. Propanoic acid caused an uncompetitive mode of inhibition (K_i=0.14?mM), however, the pyruvic, acrylic, 2-oxo-butanoic and 2-oxo-octanoic acids showed a competitive manner of inhibition with the inhibition constants (K_i) of 0.36, 0.6, 3.6 and 4.5?mM, respectively. So, it seems that, there is a physical difference in the docking of mono- and o-diphenols to the tyrosinase active site. This difference could be an essential determinant for the course of the catalytic cycle. Monophenols are proposed to bind only the oxyform of the tyrosinase. It is likely that the binding of acids occurs through their carboxylate group with one copper ion of the binuclear site. Thus, they could completely block the cresolase reaction, by preventing monophenol binding to the enzyme. From an allosteric point of view, n-alkyl acids may be involved in activation of MT catecholase reactions.     

Inhibition by N′-nitrosonornicotine of the catalytic activity of glutamate dehydrogenase in α-ketoglutarate amination

The effect of N′-nitrosonornicotine (NNN), one of the tobacco-specific nitrosamines, on the catalytic activity of glutamate dehydrogenase (GLDH) in the α-ketoglutarate amination, using reduced nicotinamide adenine dinucleotide as coenzyme, was studied by a chronoamperometric method. The maximum reaction rate of the enzyme-catalyzed reaction and the Michaelis-Menten constant, or the apparent Michaelis-Menten constant, were determined in the absence and presence of NNN. NNN remarkably inhibited the bio-catalysis activity of GLDH, and was a reversible competitive inhibitior with K_i, estimated as 199?μmol?l^?1 at 25°C and pH 8.0.     

Columbin inhibits cholesterol uptake in bloodstream forms of Trypanosoma brucei-A possible trypanocidal mechanism

The diterpenoid furanolactone (columbin) from Aristolochia albida inhibited growth of culture forms of Trypanosoma brucei. In vitro analysis of the compound at 5–250 μg/ml showed complete lysis of the parasites within 10–20 minutes post incubation. At 50 μg/ml, columbin killed about 50% of the parasites which initially appeared swollen under phase contrast microscopy. Also the total amount of cholesterol diminished dose-dependently in the presence of 10–100 μg/ml of columbin after a 3-day incubation period.

In vivo analysis of the compound in T. brucei-infected mice revealed that 25 mg/kg administered for 3 consecutive days, completely cleared the parasites from the peripheral circulation. However, columbin could not clear parasites in the cerebrospinal fluid.     

Synthesis,characterization and biological evaluation of novel 4′-fluoro-2′-hydroxy-chalcone derivatives as antioxidant,anti-inflammatory and analgesic agents

Abstract

In an effort to develop safe and potent anti-inflammatory agents, a series of novel 4′-fluoro-2′-hydroxychalcones 5a–d and their dihydropyrazole derivatives 6a–d was prepared. It was synthesized via aldol condensation of 4′-fluoro-2′-hydroxyacetophenone with appropriately substituted aldehydes followed by cyclization with hydrazine hydrate. All the synthesized compounds were evaluated for their antioxidant, anti-inflammatory, cyclooxygenase inhibition selectivity and analgesic activities. The dimethoxychalcone 5a and its dihydropyrazole derivative 6a showed the highest antioxidant activity, while the monomethoxychalcone 5d and its dihydropyrazole derivative 6d showed the highest analgesic and anti-inflammatory activities. It was also found that there is a close correlation between 4′-fluoro-2′-hydroxychalcones 5a–d and their dihydropyrazole derivatives 6a–d in the screened biological activities. To explain the correlation between the synthesized chalcones and their dihydropyrazole derivatives, especially for the anti-inflammatory activity, docking studies were performed.     

Novel Inhibitors of Enkephalin-Degrading Enzymes II: N5-Substituted-4-Thioxohydantoic Acids as Aminopeptidase Inhibitors

Abstract

Some 2-substituted-(2′-aminophenyl)-4-thioxohydantoic acids (o-amino PTC-amino acids) have antinociceptive activity when administered (icv) alone (IC₅₀ = 0.04-0.87 μM/animal) and show a striking prolongation of the antinociceptive action of (D-Ala-² D-Leu⁵)-enkephalin (DADL) in combination. The effects are thought to be mediated via opioid receptors since they are naloxone-reversible. Although inhibitors of the enkephalin degrading puromycin-insensitive, bestatin-sensitive aminopeptidase (possibly aminopeptidase M) their action is weak (IC₅₀ = 32μM leucine, 536μM, glycine) and they might be considered to have a direct antinociceptive effect on opioid receptors. The titled compounds constitute novel ‘lead’ compounds for the development of potent aminopeptidase M inhibitors.     

Kinetic Formulations for the Reduction of Ketomalonate by Lactate Dehydrogenase

Abstract

Initial rate kinetic studies of lactate dehydrogenase with ketomalonate and NADH as substrates suggest that this enzymatic system is adapted to a rapid equilibrium ordered bi-bi ternary complex mechanism. The application of the reaction product inhibition method reveals the existence of the enzyme-NADH-hydroxy-malonate and enzyme-NAD⁺-ketomalonate abortive complexes. This kinetic behaviour is confirmed by the differential inhibition induced by several alternate products on the pyruvate-lactate dehydrogenase-NADH and ketomalonate-lactate dehydrogenase-NADH systems.     

In vitro cytotoxic,antibacterial, antifungal and urease inhibitory activities of some N4- substituted isatin-3-thiosemicarbazones

A series of 15 previously reported N⁴-substituted isatin-3-thiosemicarbazones 3a-o has been screened for cytotoxic, antibacterial, antifungal and urease inhibitory activities. Compounds 3b, 3e and 3n proved to be active in cytotoxicity assay; 3e exhibited a high degree of cytotoxic activity (LD₅₀ = 1.10 × 10^{? 5} M). Compound 3h exhibited significant antibacterial activity against B. subtilis, whereas compounds 3a, 3k and 3l displayed significant antifungal activity against one or more fungal strains i.e. T. longifusus, A. flavus and M. canis. In human urease enzyme inhibition assay, compounds 3g, 3k and 3m proved to be the most potent inhibitors, exhibiting relatively pronounced inhibition of the enzyme. These compounds, being non-toxic, could be potential candidates for orally effective therapeutic agents to treat certain clinical conditions induced by bacterial ureases like H. pylori urease. This study presents the first example of inhibition of urease by isatin-thiosemicarbazones and as such provides a solid basis for further research on such compounds to develop more potent inhibitors.     

Sevoflurane modulates the activity of glyceraldehyde 3-phosphate dehydrogenase

The mechanism of inhalation anesthesia remains to be fully elucidated. While certain neuronal membrane proteins are considered sites of action, cytosolic proteins may also be targets. We hypothesize that inhaled anesthetics may act via glyceraldehyde 3-phosphate dehydrogenase (GAPDH), which has recently been shown to participate in neuronal inhibition. We examined the effects of sevoflurane, a halogenated ether anesthetic, on the catalytic and fluorescence properties of GAPDH. Initial rates of oxidoreductase activity decreased approximately 30% at saturating levels of sevoflurane. NADH-stimulated oxidoreductase activity (25 μM NADH; 0.8 mM NAD⁺) increased with sevoflurane. Sevoflurane quenched tryptophan fluorescence emission and increased polarization. Additionally, sevoflurane increased the susceptibility of GAPDH to thermal denaturation suggesting an effect on conformation. Our findings warrant further research on sevoflurane's effect on GAPDH and indicate that this approach may lead to delineation of a novel contribution to the mechanism of anesthesia.     

Tyrosinase inhibitory activities of the compounds isolated from Neolitsea aciculata (Blume) Koidz.

This study was designed to investigate the mushroom tyrosinase inhibitory activity for the constituents isolated from Neolitsea aciculata. The stems of N. aciculata was extracted with aqueous ethanol and subjected to chromatographic separation, which led to the isolation of 11 compounds: methyl linoleate (1), catechin (2), epicatechin (3), afzelin-7-O-glucopyranoside (4), 2′,3′-di-(p-coumaroyl)afzelin (5), 2′-p-coumaroylafzelin (6), feruloyl tyramine (7), β-sitosterol (8), daucosterol (9), oleic acid (10), and trilaurin (11). Their structures were elucidated on the basis of spectroscopic studies as well as by comparison with the data available in the literature. Among these isolates, compounds 5 and 6 were identified as potent mushroom tyrosinase inhibitors with IC₅₀ values of 0.067 and 0.080 mM, respectively. The inhibition kinetics, analysed by Lineweaver–Burk plots, indicated that compounds 5 and 6 are competitive tyrosinase inhibitors when using l-tyrosine as a substrate. Notably, compounds 1–11 were isolated for the first time from this plant. These results provide evidence that this plant might be a potential source of anti-melanogenesis agents.     

(3,4-Dihydroxyphenyl)(2,3,4-trihydroxyphenyl)methanone and its derivatives as carbonic anhydrase isoenzymes inhibitors

In this study, we have synthesised (3,4-dihydroxyphenyl)(2,3,4-trihydroxyphenyl)methanone and a series of its derivatives (5, 13–16) and tested the ability of these compounds to inhibit two metalloenzyme human carbonic anhydrase (hCA, EC 4.2.1.1) isozymes, hCA I and hCA II. The synthesised compounds showed inhibitory effect on hCA I and hCA II isozymes. The results showed that synthesised compounds (5, 13–16) demonstrated the best inhibition activity against hCA I (IC₅₀: 3.22–54.28 μM) and hCA II (IC₅₀: 18.52–142.01 μM). The compound 14 showed the highest inhibiton effect against hCA I (IC₅₀: 3.22 μM; K_i: 1.19?±?1.4 μM). On the other hand, the compound 13 showed the highest inhibiton effect against hCA II (IC₅₀: 18.52 μM; K_i: 3.25?±?1.13 μM).