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G A Levvy

Publications and source records attributed to G A Levvy.

At least 19 recordsLinked to original sources
PubMed1970

Purification and properties of alpha-D-mannosidase from the limpet, Patella vulgata.

1. alpha-Mannosidase from the limpet, Patella vulgata, was purified nearly 150-fold, with 40% recovery. beta-N-Acetylglucosaminidase was removed from the preparation by treatment with ethanol. The final product was virtually free from beta-galactosidase. 2. Limpet alpha-mannosidase was assayed at pH3.5 and at this pH it was necessary to add Zn(2+) for full activity. At pH5, the enzyme had the same activity in the presence or absence of added Zn(2+). 3. On incubation at acid pH, the enzyme underwent reversible inactivation, which was prevented by adding Zn(2+). 4. EDTA accelerated inactivation and the addition of Zn(2+) at once restored activity. No other cation was found to reactivate the enzyme. 5. Cl(-) had an unspecific effect on hydrolysis by limpet alpha-mannosidase. It increased the rate of reaction with substrate. The anion did not prevent or reverse inactivation by EDTA. 6. It is concluded that alpha-mannosidase is a metalloenzyme or enzyme-metal ion complex, dissociable at the pH of activity, and that it requires Zn(2+) specifically.

Animals↗
PubMed1969

Purification and properties of alpha-D-mannosidase from rat epididymis.

1. alpha-d-Mannosidase from rat epididymis was purified 300-fold. beta-N-Acetyl-glucosaminidase and beta-galactosidase were removed from the preparation by treatment with pyridine. Zn(2+) was added during the purification to stabilize the alpha-mannosidase. 2. Mammalian alpha-mannosidase is most stable at pH6. At lower pH values it undergoes reversible spontaneous inactivation. The enzyme is also subject to irreversible inactivation, which is delayed by the addition of albumin. 3. Reversible inactivation of alpha-mannosidase is accelerated by EDTA and reversed or prevented by Zn(2+). Other cations, such as Co(2+), Cd(2+) and Cu(2+), accelerate inactivation and the action of a toxic cation can be prevented by Zn(2+) or by EDTA in suitable concentration. 4. The enzyme is stabilized by substrate and neither Zn(2+), EDTA nor a toxic cation has more than a small effect in the assay of an untreated preparation. The addition of Zn(2+) is necessary, however, for a constant rate of hydrolysis during prolonged incubation of the enzyme with substrate. In an EDTA-treated preparation, Zn(2+) reactivates the enzyme during the assay. 5. Evidence is presented that alpha-mannosidase is a dissociable Zn(2+)-protein complex, in which Zn(2+) is essential for enzyme activity.

Acetone↗
PubMed1969

The enzymic degradation of ovalbumin and its glycopeptides.

1. Ovalbumin glycopeptides, freed from all amino acids other than aspartic acid and a small proportion of leucine by repeated digestion with Pronase, were hydrolysed by 1-aspartamido-beta-N-acetylglucosamine amidohydrolase (glycoaspartamidase) to the corresponding oligosaccharides. The glycoaspartamidase did not attack ovalbumin itself. 2. Ovalbumin, with mannose/hexosamine ratio 5:4, lost 1.5moles of N-acetylglucosamine and more than 2moles of mannose after incubation with alpha-mannosidase and beta-N-acetylglucosaminidase respectively. 3. In ovalbumin glycopeptides with approximate mannose/hexosamine ratios 5:3 and 5:4, one and two N-acetylglucosamine residues respectively were accessible to the action of beta-N-acetylglucosaminidase. 4. A mixture of alpha-mannosidase and beta-N-acetylglucosaminidase, acting on an ovalbumin glycopeptide with mannose/hexosamine ratio 5:3.7, removed nearly 4moles of mannose and 1.5moles of N-acetylglucosamine. 5. alpha-Mannosidase removed about 1.5moles of mannose from the ovalbumin oligosaccharide with mannose/hexosamine ratio approx. 5:3. The subsequent action of beta-N-acetylglucosaminidase liberated less than 1mole of N-acetylglucosamine and made at least 1mole further of mannose accessible to alpha-mannosidase action. 6. It is concluded that the carbohydrate moiety of ovalbumin is linked through a glycosyl group to asparagine. In a molecule with mannose/hexosamine ratio 5:4, there are two beta-N-acetylglucosamine residues linked together in a terminal position, followed by alpha-mannose. There is also present a side chain containing two alpha-mannose units.

Amidohydrolases↗
PubMed1968

Inhibition of glycosidases by aldonolactones of corresponding configuration. The specificity of alpha-L-arabinosidase.

1. The previous study (Conchie, Gelman & Levvy, 1967b) of the specificity of beta-glucosidase, beta-galactosidase and beta-d-fucosidase in barley, limpet, almond emulsin and rat epididymis was extended to alpha-l-arabinosidase. 2. The inhibitory action of l-arabinono-(1-->5)-lactone was tested against all four types of enzyme, and alpha-l-arabinosidase was examined for inhibition by glucono-, galactono- and d-fucono-lactone. 3. In emulsin, the enzyme that hydrolyses beta-glucosides, beta-galactosides and beta-d-fucosides also hydrolyses alpha-l-arabinosides. Rat epididymis resembles emulsin except that, as already noted, it lacks beta-glucosidase activity. 4. In the limpet, alpha-l-arabinosidase activity is associated with the enzyme that hydrolyses beta-glucosides and beta-d-fucosides, and not with the separate beta-galactosidase. 5. The effects of the different lactones on the barley preparation suggest that alpha-l-arabinosidase activity is associated with the beta-galactosidase rather than with the enzyme that hydrolyses beta-glucosides and beta-d-fucosides. Fractionation and heat-inactivation experiments indicate that there is also a separate alpha-l-arabinosidase in the preparation.

Aldehydes↗
PubMed1968

Purification and properties of alpha-D-mannosidase from jack-bean meal.

1. alpha-Mannosidase from jack-bean meal was purified 150-fold. beta-N-Acetyl-glucosaminidase and beta-galactosidase were removed from the preparation by treatment with pyridine. Zn(2+) was added during the purification to stabilize the alpha-mannosidase. 2. At pH values below neutrality, alpha-mannosidase undergoes reversible spontaneous inactivation at a rate dependent on the temperature, the degree of dilution and the extent of purification. The enzyme is also subject to irreversible inactivation, which is prevented by the addition of albumin. 3. Reversible inactivation of alpha-mannosidase is accelerated by EDTA and reversed or prevented by Zn(2+). Other cations, such as Co(2+), Cd(2+) and Cu(2+), accelerate inactivation; an excess of Zn(2+) again exerts a protective action, and so does EDTA in suitable concentration. 4. Neither Zn(2+) nor EDTA has any marked effect in the assay of untreated enzyme. In an EDTA-treated preparation, however, Zn(2+) reactivates the enzyme during assay. 5. It is postulated that alpha-mannosidase is a dissociable Zn(2+)-protein complex in which Zn(2+) is essential for enzyme activity.

Albumins↗
PubMed1967

Inhibition of glycosidases by aldonolactones of corresponding configuration: Preparation of (1-->5)-lactones by catalytic oxidation of pyranoses and study of their inhibitory properties.

1. A method was devised for the preparation of (1-->5)-lactones from pyranose sugars and uronic acids by platinum-catalysed oxidation with gaseous oxygen in aqueous solution at acid pH. It was applied to mannose, N-acetylglucosamine, N-acetylgalactosamine, glucuronic acid, galacturonic acid, galactose, l-arabinose and d-fucose. 2. Only the first three yielded products that could be obtained in the solid state without decomposition. In every case, however, the oxidation product in aqueous solution behaved as the aldono-(1-->5)-lactone, and was more inhibitory towards the appropriate glycosidases than any aldonolactone preparation hitherto examined. 3. The stabilities of the oxidation products were studied, and their interconversion with the (1-->4)-lactones was demonstrated. Ring-opening does not appear to be mandatory for this isomeric change, which in some instances is very rapid. 4. To explain all the inhibitory effects observed with aldonolactones on glycosidases of corresponding configuration, it is tentatively postulated that inhibition may be due entirely to the (1-->5)-lactone, and that any inhibitory effect seen with the (1-->4)-lactone is a measure of the extent and speed of its conversion into the (1-->5)-lactone in aqueous solution.

Journal Article↗
PubMed1967

Inhibition of glycosidases by aldonolactones of corresponding configuration. The C-4- and C-6-specificity of beta-glucosidase and beta-galactosidase.

1. In barley, beta-glucosidase and beta-galactosidase are separate enzymes. The former also displays beta-d-fucosidase activity. 2. In the limpet, Patella vulgata, beta-glucosidase activity is associated with the beta-d-fucosidase, previously shown to be a separate entity from the beta-galactosidase also present. 3. Almond emulsin presents all three activities as a single enzyme. Each is equally inhibited by glucono-, galactono- and d-fucono-lactone. 4. In rat epididymis, there is no significant beta-glucosidase activity, nor is there appreciable inhibition of the beta-galactosidase and beta-d-fucosidase activities of the preparation by gluconolactone.

Animals↗