N,S-bis-fluorenylmethoxycarbonylglutathione: a new, very potent inhibitor of mammalian glyoxalase II.

A very potent competitive inhibitor of mammalian glyoxalase II activity, N,S-bis-fluorenylmethoxycarbonylglutathione (DiFMOC-G) has been synthesized and characterized. The Ki value for inhibition of glyoxalase II purified from calf liver is 0.08 microM. The Ki values for glyoxalase I inhibitions range from 285 to 500 fold higher than the values obtained for glyoxalase II inhibitions, depending on the source of the enzyme. Among other enzymes involved in glutathione metabolism, such as glutathione S-transferase, glutathione reductase, and glutathione peroxidase, only glutathione S-transferase is inhibited to a small extent by DiFMOC-G. Diesters of DiFMOC-G were prepared in order to improve transport of DiFMOC-G into mammalian tumor cells (rat adrenal pheochromocytoma, PC-12) in culture. Among the diesters synthesized, diisopropyl DiFMOC-G was found to be the most inhibitory to cell viability, with a [I]0.5 value of 3 microM.

S-fluorenylmethoxycarbonyl glutathione and diesters: inhibition of mammalian glyoxalase II.

Inhibitors having high specificity toward mammalian glyoxalase II, but not glyoxalase I, were sought as part of a program to study glyoxalase enzyme function in mammalian cells. The compound, S-fluorenylmethoxycarbonyl glutathione (FMOC-G), was synthesized and found to be a competitive inhibitor of purified calf liver glyoxalase II (Ki = 2.1 mumol/l). Inhibition constants (Ki values) for the other glyoxalase enzyme, glyoxalase I, and the glutathione-requiring enzyme, glutathione S-transferase, from other sources, were found to be 17 and 25 mumol/l, respectively. FMOC-G is a very poor inhibitor of glutathione reductase and glutathione peroxidase. Diesters (dimethyl, diethyl, diisopropyl) of FMCO-G were also synthesized, as proinhibitors, to improve transport of FMOC-G into mammalian tumor cells (rat adrenal pheochromocytoma, PC-12) in culture. The diesters were inhibitory to cell growth and variability; the most effective of these, diisopropyl FMOC-G, exhibited an [I]0.5 value of approximately 275 mumol/l. Diesters of FMOC-G may be useful in studies of the glyoxalase enzyme system in cultured mammalian cells.

Inhibition of hepatic xenobiotic metabolism and of glutathione-dependent enzyme activities by zinc ethylene-bis-dithiocarbamate in the rabbit.

Effects of either a single (300 mg/kg) or a subchronic (0.3 and 0.6% for 70 days) oral administration of a dithiocarbamate fungicide (zinc ethylene-bis-dithiocarbamate, zineb) on hepatic drug metabolism and on the activity of several glutathione-dependent enzymes were investigated in male New Zealand White rabbits. While a pronounced reduction in the rate of oxidative biotransformations occurred after either single or repeated exposure, both cytochrome P450 and total haem content were lowered following acute challenge to zineb. None of the experimental protocols affected microsomal carboxylesterase but induced a marked increase in glutathione content and none of the examined glutathione-dependent enzymes was altered by the single administration of zineb, whereas the subchronically exposed rabbits showed a fall in the activities of both total glutathione S-transferase and selenium-independent glutathione peroxidase. In the 0.6% treated animals, a decrease in class mu glutathione S-transferase and glyoxalase I, and an increase in thiol-transferase activities were also recorded. It is concluded that (1) zineb is able to selectively impair oxidative drug metabolism with possible different mechanism(s) according to the duration of the exposure, (2) only the subchronic treatment affects glutathione-dependent enzymes, (3) the decrease in glutathione S-transferase activity would seem to be ascribed to a direct interaction with the fungicide.

Dimeric forms of cholinesterase in Sipunculus nudus.

In developing a research on the cholinesterase (ChE) evolution in Invertebrata, this enzyme was studied in the unsegmented marine worm Sipunculus nudus. ChE activity was solubilized through three successive steps of extraction. These fractions are noted as low-salt (LSS), detergent (DS) and high-salt soluble (HSS) and represent 27%, 68% and 5% of total activity, respectively. LSS and DS ChE were purified to homogeneity by affinity chromatography on edrophonium-Sepharose gel. Purification factors of 1700 (LSS) and 1090 (DS) were obtained. The small amount of HSS ChE prevented a similar purification and an extensive characterization. Based on SDS/PAGE and density-gradient centrifugation, both LSS and DS enzymes show a M(r) value of about 130,000 and are likely G2 globular dimers of a 67,000 subunit. Moreover, LSS ChE seems to be an amphiphilic form including a hydrophobic domain, while DS ChE is probably linked to the cell membrane by a phosphatidylinositol anchor. Both LSS and DS enzymes hydrolyze at the highest rate propionylthiocholine. However, they also show a fairly high catalytic efficiency with other thiocholine esters as substrates, thus suggesting a wide and little-specialized conformation of the active site. Based on immunological cross-reactivity trials, LSS and DS ChE from S. nudus show a reduced structural affinity with a molluscan (Murex brandaris) enzyme. HSS ChE, an acetylcholinesterase, is also solubilized by heparin, like typical vertebrate HSS asymmetric enzymes. However, it lacks fast-sedimenting forms and an enzyme-anchoring collagenous structure.

Presence of glyoxalase II in mitochondria from spinach leaves: comparison with the enzyme from cytosol.

Glyoxalase II has been purified from cytosol and mitochondria of spinach leaves. Electrophoresis and isoelectric focussing have resolved cytosolic and mitochondrial glyoxalase II in multiple forms: pl 5.3, 5.8 and 6.2 (cytosol) and pl 4.8 (mitochondria). The enzyme of both localizations is a monomer showing a relative molecular mass of about 26 kDa. The values of kinetic constants using several glutathione thiolesters as substrates, are similar for the enzymes from cytosol and mitochondria. These results extend also to plant the presence in mitochondria of peculiar forms of glyoxalase II, likewise recently demonstrated in mammalians.

Glyoxalase I and glyoxalase II from Aloe vera: purification, characterization and comparison with animal glyoxalases.

Glyoxalase I and glyoxalase II from the outer green rind of Aloe vera leaves were purified by (matrix) affinity ligand-enzyme binding methods. The purified enzymes exhibited single protein bands on SDS-PAGE electrophoresis, with MW values of approximately 44,000 and 27,000 for glyoxalase I and glyoxalase II, respectively. The glyoxalase I is a basic protein (pI 7.8), while the glyoxalase II (3 protein bands) is acidic (pI 4.7, 4.8 [prevalent form], and 5.0). The kinetic constants, Km and Vmax, and Ki values for certain inhibitors are reported for both glyoxalase I and glyoxalase II. The glyoxalase enzymes from Aloe vera were compared with reported animal and plant glyoxalases.

Induction of mouse liver glyoxalase I by hypobaric hypoxia.

Hypobaric hypoxia at 0.45 atm induced a reversible increase of mouse liver glyoxalase I. The levels of this enzyme increased after an exposure of 20 h and 20 + 20 h, whereas the activity decreased to the control values after 20 h at room pressure. Before the treatment, some animals received tritiated leucine (i.p.). Glyoxalase I was purified to homogeneity. The pure enzyme from the treated animals showed 20-times more radioactivity than the controls. Thus, the increase in specific activity is due to new protein synthesized in response to the treatment at 0.45 atm. The activities of glyoxalase II and glutathione S-transferase were not affected by the treatment.

Presence of a plant-like glyoxalase II in Candida albicans.

Glyoxalase II from Candida albicans was purified by affinity chromatography on S-carbobenzoxyglutathione-Affi Gel 10. The enzyme was characterized and compared with the glyoxalases II from animal and plant sources. The relative molecular mass is 29 kDa, and the isoelectric point (pI) is 6.0. The acidic pI value appears to be typical for plant glyoxalase II, in contrast to the uniformly basic glyoxalase II pI values from animals. S-D-Lactoylglutathione and S-acetoacetylglutathione are the best substrates, and S-carbobenzoxyglutathione is the best inhibitor of the yeast enzyme. Glutathione derivatives with a thioether bond are not inhibitory. Glyoxalase II from Candida albicans is compared either with animal and plant enzymes.

Isolation of glyoxalase II from bovine liver mitochondria.

Bovine liver mitochondria contain about 10% of the total glyoxalase II activity in the homogenate. Electrophoresis and isoelectric focussing of either crude mitochondrial extract or the purified mitochondrial glyoxalase II resolved the enzyme activity into five forms (pl 6.3, 6.7, 7.1, 7.7, and 7.9). Since bovine liver cytosol contains a single form of glyoxalase II (pl 7.5), at least four forms are exclusively mitochondrial with no counterpart in the cytosol. The relative molecular mass of mitochondrial glyoxalase II is about 23-24 kDa, similar to the cytosolic form. The kinetic constants obtained using S-D-lactoyl, S-acetyl-, S-acetoacetyl-, and S-succinyl-glutathione as substrates are similar to those reported for glyoxalase II from rat liver mitochondria. S-D-Lactoyl- and S-acetoacetyl-glutathione are the best substrates. S-Acetylglutathione is the poorest substrate with respect to both Vmax and Km values.

Effects of some S-blocked glutathione derivatives on the prevalent glyoxalase II (a form) of rat liver.

The prevalent glyoxalase II (S-2-hydroxyacylglutathione hydrolase, EC 3.1.2.6, a form) of rat liver cytosol has been studied with a series of seven S-blocked glutathione derivatives. At pH 7.4 and 20 degrees C, only p-nitrobenzyl-S-glutathione was found completely inactive. All the other derivatives are linear competitive inhibitors of the enzyme. Ki values using S-D-lactoylglutathione as substrate are reported. Alkyl-S-glutathiones are weak inhibitors and their inhibition increases with the decrease of the length of the alkyl chain. The best inhibitors are those glutathione derivatives which contain a thioester bond (carbobenzoxy- and p-nitrocarbobenzoxy-S-glutathione) or a carbonyl group (p-chlorophenacyl-S-glutathione). Inhibition by carbobenzoxy-S-glutathione seems to be more complex since the double reciprocal plot shows deviation from linearity at low substrate concentration.

Glyoxalase II from Zea mays: properties and inhibition study of the enzyme purified by use of a new affinity ligand.

The synthesis of N-(p-nitrocarbobenzoxy)glutathione (N-pNCBG) is reported. N-pNCBG and glutathione (GSH) were coupled to Affi-gel 10 by a thioester linkage and resulted in very effective bound ligands for a fast purification of glyoxalase II from corn. The S-(N-pNCBG)-affinity column showed a glyoxalase II binding capacity of up to 2-fold higher than that of the glutathione-affinity column. A single form of glyoxalase II was evidenced by PAGE in both crude extracts and in the affinity purified enzyme. A 45% recovery of glyoxalase II activity (purification, approx. 433-fold) was obtained for both matrices by a single chromatography. The purified glyoxalase is an acidic protein (pI 4.5) of about 26,000 relative molecular mass. Substrate studies for the corn glyoxalase II show, among possible substrates tested, that S-D-lactyl-glutathione is the preferred substrate. An inhibition study was performed with methyl-, propyl-, hexyl-, p-nitrobenzyl-, p-chlorophenacyl-, carbobenzoxy-, and p-nitrocarbobenzoxy-S-glutathione. Methyl-S-glutathione did not inhibit corn glyoxalase II; the others were found to be linear competitive inhibitors. The derivatives containing a thioether bond are weaker inhibitors than those containing a thioester bond or a carbonyl group. p-Nitrobenzyl-S-glutathione is the weakest inhibitor; the carbobenzoxy-S-derivatives are stronger inhibitors than the p-chlorophenacyl S-derivative.

Relaxed thiol substrate specificity of glutathione transferase effected by a non-substrate glutathione derivative.

Rat glutathione transferase 4-4 catalyzed the conjugation of 2-mercaptoethanol with 1-chloro-2,4-dinitrobenzene in the presence of S-methyl-glutathione. The reaction was linearly dependent on enzyme concentration and saturation was seen with respect to both 2-mercaptoethanol and S-methyl-glutathione concentration. High concentrations of S-methyl-glutathione were inhibitory. The results suggest that the natural substrate glutathione has two distinct functions in the normal catalytic reaction, (i) induction of a catalytically competent conformation of the enzyme and (ii) provision of the substrate sulfhydryl group in the reaction catalyzed.

Purification and characterization of two forms of glyoxalase II from the liver and brain of Wistar rats.

Glyoxalase II (S-(2-hydroxyacyl)glutathione hydrolase, EC 3.1.2.6) was purified to homogeneity and separated into two forms (alpha, pI = 8.0; beta, pI = 7.4) from both liver and brain of wistar rats by column isoelectric focusing. These forms were also found to have different electrophoretic mobilities. No significant differences were found between the alpha and beta forms from either source in the relative molecular mass (about 24,000) or in Km values using three substrates. The temperature-inactivation profiles were also similar, the two forms being stable up to 50 degrees C. Chemical modification studies with phenylglyoxal suggest that these enzyme forms probably contain arginine residues near the active site. Inactivation of alpha and beta forms by diethylpyrocarbonate and by photooxidation with methylene blue, and protection by S-D-mandeloylglutathione, a slowly reacting substrate, suggest the presence of histidine at the active site. The alpha and beta forms show different half-life values in inactivation by histidine reagents, which may be due to a difference in the active-site structures of these enzymes. The results probably indicate distinct structures (sequences) for alpha and beta forms.

A comparative study on glyoxalase II from vertebrata.

S-2-hydroxyacylglutathione hydrolase (glyoxalase II) from the liver of animals belonging to the various vertebrate classes (Oryctolagus cuniculus, Gallus gallus, Python molurus, Rana esculenta, Esox lucius) have been purified from 100,000 g supernatants of liver homogenates, using acetone fractionation and affinity chromatography. Subsequent comparative studies were concerned with some molecular and kinetic properties. Isoelectric focusing gave evidence for a single form of liver glyoxalase II in O. cuniculus, P. molurus and E. lucius, while the enzyme from G. gallus and R. esculenta showed respectively two and three forms with different pI values. All studied enzymes are basic proteins. The relative molecular mass values range from 18,000 to 23,000. The various glyoxalases II do not display markedly different Kn or Ki values. Their stability behavior at different temperatures is also quite similar.

Alkaline phosphatase in Hirudo medicinalis L.: partial purification and study of certain molecular and catalytic properties.

The authors carried out extraction and purification of an alkaline phosphatase (AP) from Hirudo medicinalis and studied certain characteristics of the enzyme. After homogenizing specimens of H. medicinalis and centrifuging the homogenate at 70,000 g, the enzyme, likely membrane-bound, was obtained in a soluble form by treating the sediment with n-butanol. It was then purified by acetone fractionation and Sephadex G-200 chromatography. A fairly good purification degree was achieved; the enzyme appears to be in a single form and displays a molecular weight of about 268,000. The optimum pH (9.5) is lower than the ones generally observed as regards APs from both Invertebrata and Mammalia. The studied AP displays a strong substrate inhibition, similar to that concerning Metazoa at a higher evolutionary level (Mollusca, Echinodermata). On the contrary, the enzyme-substrate affinity, as shown by Km value (2.447 mM), is lower than as regards APs from more advanced organisms (Echinodermata, Mammalia).