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Biomedical subjects

L Kiss

Publications and source records attributed to L Kiss.

At least 73 records · Page 4Linked to original sources
PubMed1996

Evaluation of C-(beta-D-galactosyl) and C-(2-deoxy-D-lyxo-hex-1-enopyranosyl) (D-galactal type) derivatives as inhibitors of beta-D-galactosidase from Escherichia coli.

C-(2-Deoxy-D-lyxo-hex-1-enopyranosyl)formamide was prepared from acetylated C-(beta-D-galactopyranosyl)formamide by a radical-mediated bromination-zinc/N-methylimidazole-induced reductive elimination-Zemplén deacetylation reaction sequence. The preparation of acetylated 5-(2-deoxy-D-lyxo-hex-1-enopyranosyl)tetrazole was improved. Methyl C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formimidate was transformed by benzylamine into N-benzyl-C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formamidine and, after hydrolysis to methyl C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formate, into N-benzyl-C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formamide. A series of C-(beta-D-galactopyranosyl) and C-(2-deoxy-D-lyxo-hex-1-enopyranosyl) derivatives was comparatively investigated for E. coli beta-D-galactosidase inhibitory activity. N-Benzyl-C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formamidine was the best inhibitor and had K(i) = 6 microM (on the basis of its free base concentration, K(i) = 8.3 nM was obtained). Basicity and hydrophobicity of the aglycon proved to be more important factors for the inhibition than the conformation of the sugar ring.

Carbohydrate Conformation↗
PubMed1996

Co-purification from Escherichia coli of a plant beta-glucosidase-glutathione S-transferase fusion protein and the bacterial chaperonin GroEL.

The coding sequence of the mature cyanogenic beta-D-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) (linamarase) of Manihot esculenta Crantz (cassava) was cloned into the vector pGEX-2T and expressed in Escherichia coli. The bacterial chaperonin GroEL [Braig, Otwinowski, Hedge, Boisvert, Joachimiak, Horwich and Sigler (1994) Nature (London) 371, 578-586] was found to be tightly associated with the fusion protein and co-purified with it. In the presence of excess MgATP, release and folding of the fusion beta-glucosidase were demonstrated by a fast increase in both linamarase and p-nitrophenyl-beta-D-glucopyranosidase activity at a low protein concentration. A slow endogenous folding process was also detected by activity measurements. Michaelis constants (Km) and the ratio between the maximal velocities and efficiency constants (Vmax., Vmax./Km) for the hydrolysis of the natural substrate, linamarin, and p-nitrophenyl beta-D-glucopyranoside (PNP-Glc) by the recombinant protein were found to be almost identical with those of the native glycosylated plant enzyme [Keresztessy, Kiss and Hughes (1994) Arch. Biochem. Biophys. 314, 142-152]. Molecular dissociation constants for the free enzyme (pK(E)1, pK(E)2) obtained with linamarin and PNP-Glc, and the enzyme substrate complexes (pK(ES)1, pK(ES)2) were also in accordance with that of the original protein. The reactive substrate analogue N-bromoacetyl beta-D-glucosylamine inactivated the fusion enzyme according to pseudo-first-order kinetics with first-order rate constant (k1=0.007 min-1) and apparent inhibition constants (k1=20 mM) comparable with those of the plant protein [Keresztessy, Kiss and Hughes (1994) Arch. Biochem. Biophys. 315, 323-330]. In comparison with the native glycosylated plant protein, the recombinant protein was, however, found to be extremely sensitive to proteolysis and misfolding.

Acetylglucosamine↗
PubMed1996

Coagulase-negative staphylococci in air samples from operating theatres.

The aim of our study was to recognize coagulase-negative staphylococci (CNS) in the air of operating theatres. Out of the identification of 449 isolates, the most frequent species were Staphylococcus epidermidis and Staphylococcus haemolyticus. The strains were adherent to glass in 52.3%. Most of the S. epidermidis showed adherent growth, while the majority of the S. haemolyticus failed to adhere. The disk-diffusion antibiotic sensitivity tests showed great differences in sensitivity to penicillin, tetracycline and erythromycin between adherence-positive and negative isolates. On the whole, the species S. haemolyticus proved to be much more resistant than S. epidermidis. Staphylococcus warneri was the most, while S. haemolyticus was the least sensitive to phages.

Air Microbiology↗
PubMed1995

[The effect of captopril on the acidification function of the kidney in hypertension].

The effect of the converting enzyme inhibition treatment on the renal acidification function was studied in 5 mild hypertensive subjects. Before and after one week treatment with daily 75 mg of captopril bicarbonate loading was carried out by peroral administration of 68 mmol NaHCO3. The difference between the partial carbon dioxide tension (pCO2) of the urine and blood [(U-B) pCO2], as well as the pH and bicarbonate values were determined at every hour in the course of 3 hours. In the same persons phosphate loadings were also carried out. Although decrease H+ excretion may follow the suppression of aldosterone, which could be expected in response to the short-term captopril treatment, no such change in distal tubular function could be demonstrated by the sensitive methods administered in this study. It seems to be highly probable, that captopril does not limit the urinary acidifying function in patients with healthy kidneys.

Administration, Oral↗
PubMed1995

Antibiotic resistance of Acinetobacter calcoaceticus strains isolated from patients treated in intensive care units.

The distribution according to specimens and susceptibility to antimicrobial agents of 481 Acinetobacter calcoaceticus strains isolated from patients treated in intensive care units were studied. They occurred most frequently in tracheal specimens and pus. Using disk diffusion test the strains proved to be multiple resistant to ampicillin (86.3%), azlocillin (86.7%), mezlocillin (84.0%), cefamandole (99.7%), cefoxitin (94.1%), cefuroxime (90.6%), cefoperazone (84.9%), cefotaxime (82.0%), ceftriaxone (81.0%), tobramycin (71.2%), gentamicin (86.2%), chloramphenicol (90.5%) and tetracycline (89.8%). Based on the lowest incidence of resistant strains imipenem (0%), netilmicin (2.6%), amikacin (4.9%), ampicillin+sulbactam (8.9%), amoxicillin+clavulanic acid (29.4%), pefloxacin (26.2%), ciprofloxacin (30.1%), ofloxacin (34.3%), cotrimoxazole (41.6%), carbenicillin (41.2%) or ceftazidime (55.4%) may be the drug of choice in nosocomial A. calcoaceticus infections.

Acinetobacter calcoaceticus↗
PubMed1994

Investigation of the active site of the cyanogenic beta-D-glucosidase (linamarase) from Manihot esculenta Crantz (cassava). I. Evidence for an essential carboxylate and a reactive histidine residue in a single catalytic center.

The broad-specificity cyanogenic beta-D-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) (linamarase) from Manihot esculenta Crantz (cassava) was kinetically characterized in mixed substrate systems and with the transition-state analogue glucono(1-5)lactone and a series of 1-thio substrate analogues. The results indicate a common catalytic and a common sugar binding site in the enzyme for all of the investigated substrates. Kinetic parameters of the hydrolysis of linamarin and p-nitrophenyl beta-D-glucopyranoside were determined over the pH range 3.5-9.0. The pH-dependence curves gave apparent pK values of 4.5 (4.6) and 7.1 (7.3) for the free enzyme, while values of 4.5 (3.7) and 9.3 were obtained for the enzyme-substrate complexes, using either linamarin or p-nitrophenyl beta-D-glucopyranoside as the substrate. Kinetic analysis of the modification indicated that one molecule of water-soluble carbodiimide or Woodward's reagent K is required to bind to the enzyme for inactivation. The enzyme was protected against inactivation by the competitive inhibitors p-nitrothiophenyl beta-D-glucopyranoside, beta-D-glucopyranosylamine, and glucono(1-5)lactone. Spectrophotometric analysis at 340 nm showed that from the three carboxylate groups modified by Woodward's reagent K essentially one was protected by p-nitrothiophenyl beta-D-glucopyranoside. During modification Vmax decreased to 30% of that of the unmodified enzyme and Km remained unchanged. The pH dependence of inactivation showed the involvement of a group with a pK value of 4.6, indicating the modification of a carboxyl residue essential for activity. Treatment of the enzyme with the histidine-group-specific reagent diethylpyrocarbonate resulted in 80% loss of enzyme activity, in biphasic kinetics. A treatment with 0.5 M hydroxylamine at pH 7.0 regenerated 92% of the original enzyme activity. The presence of the competitive inhibitor beta-D-glucopyranosylamine protected the enzyme against inactivation, preventing the modification of one histidine residue. Statistical analysis of the residual fractional activity against the number of modified residues indicated that the modification of one histidine is responsible for 40-50% of the inactivation. The pH dependence of the inactivation gave a pK value of 7.0 for the histidine group upon which the activity depends. During modification, Vmax decreased to 30% and Km decreased to 50% of the original values.

Binding Sites↗
PubMed1994

Investigation of the active site of the cyanogenic beta-D-glucosidase (linamarase) from Manihot esculenta Crantz (cassava). II. Identification of Glu-198 as an active site carboxylate group with acid catalytic function.

The broad-specificity cyanogenic beta-D-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) (linamarase) from Manihot esculenta Crantz (cassava) was irreversibly inactivated by N-bromoacetyl-beta-D-glucopyranosylamine according to pseudo-first-order kinetics with a second-order efficiency constant (ki/Ki = 0.1 min-1 M-1) identical for p-nitrophenyl-beta-D-glucopyranosidase, p-nitrophenyl-beta-D-galactopyranosidase, and linamarase activities of the enzyme. The competitive inhibitor p-nitrothiophenyl-beta-D-glucopyranoside protected the enzyme from inactivation. pH dependence of the pseudo-first-order rate constant of inactivation revealed the involvement of an amino acid side chain in the inactivation process with pKa 7.0, which is very similar to that of the acid catalyst group of the enzyme (pKE2 = 7.2). The involved amino acid, which has to be ionized for the inactivation, was identified as Glu-198 using 14C-labeled inactivator to label the enzyme, cleaving the labeled protein into peptides and then purifying and sequencing the labeled peptide. This residue is highly conserved in the homologous family A beta-glucosidases and family A1-A5 cellulases and lies in a consensus Asn-Glu-Pro motif occurring in all of these enzymes.

Acetylglucosamine↗