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Biomedical subjects

G Legler

Publications and source records attributed to G Legler.

At least 73 records · Page 4Linked to original sources
PubMed1978

Amino acid sequence at the active site of beta-glucosidase A from bitter almonds.

beta-Glucosidase A from bitter almonds was inhibited by the substrate analogue 6-bromo-3,4,5-trihydroxycyclo[2-3H]hex-1-ene oxide. Incorporation of 2 mol inhibitor/mol of dimeric enzyme resulted in total loss of activity. From tryptic digests of the labeled enzyme two radioactive peptides were isolated and their sequence determined (binding site of inhibitor underlined): peptide I, containing approx. 60% of the label: Ile-Thr-Glx-Glx-Gly-Val--Phe-Gly-Asp-Ser-Glx-(Ala, Asx2, Pro)-Lys and peptide II with approx. 30% of the label: Gly-Thr-Glx-Asp. The specifity of the reaction of beta-glucosidases (beta-D-glucoside glucohydrolase, EC 3.2.1.21) with substrate-related epoxides indicates that the aspartic acid labeled in peptide I participates in the catalytic process of beta-glucoside hydrolysis. The labeling of a second site is interpreted in terms of two, mutually exclusive, binding modes of the inhibitor.

Amino Acid Sequence↗
PubMed1977

Stereospecific ring opening of conduritol-B-epoxide by an active site asparatate residue of sucrase-isomaltase.

Conduritol-B-epoxide inactivates sucrase-isomaltase (sucrose alpha-glucohydrolase, EC 3.2.1.48-dextrin 6-alpha-glucohydrolase, EC 3.2.1.10) irreversibly with incorporation of 1 mol inhibitor/mol subunit, the affinity label being bound in both subunits to a beta-carboxyl group of an aspartic acid (Quaroni, A. and Semnza; G. (1976) J. Biol. Chem. 251, 3250-3253). Conduritol-B-epoxide is a racemic mixture of 1-L-1,2-anhydro-myo-inositol and 1-D-1,2-anhydro-myo-inositol, but only the latter one is the reactive component, since 1-L-1,2-anhydro-myo-inositol alone did not inactivate the enzyme. After inactivation by 1-D-1,2-anhydro-myo-inositol the label was released by hydroxylamine and identified as scyllo-inositol. One can decide now which C atom of the epoxide ring has been attacked by the enzyme's aspartate residue. This explains why only the D-enantiomer is the reactive species and provides further information about the role of the carboxylate residue during enzymic hydrolysis.

Animals↗
PubMed1977

Glucosidases.

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Affinity Labels↗
PubMed1975

4,4'-Dinitrodiphenyldisulfides of different charge type as probes for the electrostatic environment of sulfhydryl groups.

5,5'-Dithiobis-(2-nitro-N-trimethylbenzyl ammonium iodide) (I) and 5,5'-dithiobis-(2-nitro-N-2'-hydroxyethyl benzamide) (II) were synthesized as positively charged and neutral analogs of Ellman's reagent (5,5'-dithiobis-(2-nitrobenzoic acid) (III). Their reaction rates with a variety of thiols with different charge showed that sulfhydryl groups with no charge react about 25 times more rapidly with I than with III. A positive charge removed three single bonds from the sulfhydryl group decreases this ratio to about 3.5 to 1 while a negative charge within three single bonds increases it to 120 to 1. The reactivity of II was much higher than that of III but smaller than that of I. Comparison of the rates at 15 and 25 degrees C gave activation enthalpies (10.6-17.4 kcal/mol) that did not depend in a clear-cut way on the charge of the reacting species. Measurements at different salt concentrations showed an enhancement of the differences between I, II, and III at low ionic strength and a leveling effect of added salt.

Binding Sites↗
PubMed1975

The mechanism of action of glycosidases.

The factors that may contribute to the rate enhancement observed with enzymatic versus non-enzymatic hydrolysis of glycosides are discussed. The nature of the active site as deduced from labelling studies with beta-glucosidases is described. A two-step mechanism involving either an enzyme stabilized glycosyl ion or a covalent glycosyl-enzyme intermediate is proposed. Experiments with a beta-glucosidase from almonds show that even with 2-deoxy glucosides with good leaving groups as aglycon which are hydrolyzed 1000 times more slowly than the corresponding glucosides, the deglucosylation step is faster than the cleavage of the glycosidic bond.

Aspergillus↗