Neurotoxic effects of administration of artemisinin combination therapy (artemether and quinine) and ascorbic acid on the cytoarchitecture of the cerebellum and trapezoid nuclei in adult rats.

This study investigated the neurotoxic effects of the combined intramuscular administration of Artemether (0.5 mg/kg/b.w.), Quinine (5.14 mg/kg/b.w.) and Ascorbic acid (0.21 mg/kg/b.w) on the cerebellum, trapezoid nuclei and behavioural functions in male Wistar rats for a period of seven days. Statistical analyses showed no significant differences between the average weight of the brain and cerebellum of the experimental group compared with the control group. All experimental rats showed normal histology on completion of the experimental procedures in comparison with control rats. Histological assessment of the cerebellum and trapezoid nuclei in all groups showed normal cytoarchitecture. All rats displayed normal balance and co-ordination. This study observed that the combined therapy regime over a seven day period did not cause neurohistopathological effects on the cytoarchitecture of the cerebellum and trapezoid nuclei indicating that the current therapeutic doses of Artemether combined with Quinine used in the treatment of malaria are probably safe.

Purification and kinetic characterization of pickerel liver alcohol dehydrogenase with dual coenzyme specificity.

A major alcohol dehydrogenase isozyme that displays dual coenzyme specificity has been purified from pickerel liver by ion-exchange, gel filtration, and affinity chromatographic procedures. The purified enzyme is chromatographically and electrophoretically homogeneous. It is dimeric and possesses common physical properties shared by other liver alcohol dehydrogenases. Phosphorus-31 nuclear magnetic resonance spectroscopy demonstrates that NADP+ binds to two coenzyme sites of the pickerel enzyme. Steady-state kinetic studies suggest that pickerel liver alcohol dehydrogenase catalyzes NAD(P)(+)-linked ethanol oxidation via a random pathway. While the NADP+ reduction involves the formation of an abortive complex at high NADP+ concentrations, the NAD+ reduction at low NAD+ concentrations follows an ordered Bi-Bi mechanism with NAD+ being the leading reactant.

Multifunctional activities of pickerel liver alcohol dehydrogenase.

A major isozyme of pickerel liver alcohol dehydrogenase has been purified to homogeneity. The enzyme, in addition to catalyze NAD(P)(+)-linked dehydrogenation of alcohols, also mediates dismutation of aldehydes and hydrolysis of esters. Steady-state kinetic studies and chemical modifications of the pickerel liver enzyme with respect to its esterolytic and dismutative activities were carried out. Pickerel liver alcohol dehydrogenase catalyzes hydrolyses of p-nitrophenyl esters via a Uni-Bi mechanism, with alkanoic acids as the last product released. Modifications of Cys and Lys suppress the esterolytic activity. A random mechanism with the formation of dead-end complexes is implicated for the dismutation of octanal catalyzed by pickerel liver alcohol dehydrogenase. Two amino acid residues, Cys and His, are involved in the dehydrogenation as well as dismutation reactions. The present study identifies a regulatory function of Lys for the multifunctional activities of liver alcohol dehydrogenase. When the Lys residue is specifically glucosylated, the dehydrogenase activity increases. Its esterase activity decreases, while the dismutase activity remains unchanged.

Studies of NADP(+)-preferred secondary alcohol dehydrogenase from Thermoanaerobium brockii.

Alcohol dehydrogenase has been purified from the cell-free preparation of Thermoanaerobium brockii to homogeneity, employing combined DEAE, Sephadex, and affinity chromatographic procedures. The enzyme is tetrameric having subunit molecular weight of 40.4 x 10(3). The purified alcohol dehydrogenase is capable of utilizing either NAD+ or NADP+ to oxidize primary and secondary alcohols, although it prefers NADP+ as the coenzyme and secondary alcohols as substrates. Inactivation of the enzymic activity by sensitized photooxidation and carboxymethylation implicates the presence of catalytically important histidine and cysteine residues. Kinetic studies indicate that Thermoanaerobium alcohol dehydrogenase catalyzes NADP(+)-linked oxidations of secondary alcohols by an ordered bi-bi mechanism with NADP+ as the leading reactant. The preference of the Thermoanaerobium enzyme for NADP+ is correlated with its low dissociation constants (KA and KiA) and high turnover rate (V/Et). The corresponding kinetic parameters also contribute to the preference of this enzyme for secondary alcohols.

Purification and comparative studies of alcohol dehydrogenases.

Alcohol dehydrogenases from various animal and plant sources were purified by a common procedure which employed DEAE, Sephadex-G100 and affinity chromatographies. The procedure achieves an 80-130 fold purification for animal enzymes. However, only a 5-15 fold purification for plant enzymes was attained because of the instability of these enzymes. Purified alcohol dehydrogenases from animal and plant sources differ in coenzyme and substrate specificities. The enzymes from mammalian, avian and fish livers display aldehyde oxidizing and esterolytic activities in addition to alcohol oxidizing activity. However, the enzymes from plants and yeast show only the oxidative activity toward alcohols. Chemical modifications have been performed to identify amino acid residues which are essential to the oxidative and esterolytic activities of alcohol dehydrogenases.