PubMed Health⌕ Search

Biomedical subjects

E Balestreri

Publications and source records attributed to E Balestreri.

14 recordsLinked to original sources
PubMed1995

The inhibition of a leaf proteinase by L-lysine homopolymers.

The role of interlinked positively charged amino acids in the mechanism of inhibition of a monomeric trypsin-like proteinase has been investigated using high molecular mass L-lysine homopolymers ranging from 3.8 to 109 kDa. The data show that the degree of polymerization enhances the inhibitory efficiency which is maximal for homopolymers with more than eighteen interlinked lysine residues. The inhibition is cooperative and, under the maximal inhibition conditions, nine lysine residues of the polymer are involved in the electrostatic binding to the enzyme. A limited conformational change of the protein molecule accompanies the transition from a fully active to a fully inactivated enzyme.

Endopeptidases↗
PubMed1987

Mechanism of polyamine inhibition of a leaf protease.

The inhibition of a highly purified alfalfa (Medicago sativa) leaf protease by naturally occurring polyamines is reported. The tetraamine spermine shows the highest inhibitory effect, with the maximum inhibition at 0.1 mM. Kinetic data indicate an apparent hyperbolic competitive inhibition. CD measurements show that in the presence of 0.1 mM spermine the enzyme undergoes a conformational change with the loss of 16% alpha-helix secondary structure content. Both the inhibition and the conformational change are prevented by high ionic strength. These data suggest a novel control mechanism of proteolytic activity in the leaf.

Circular Dichroism↗
PubMed1986

Purification, stability and kinetic properties of highly purified adenosine deaminase from Bacillus cereus NCIB 8122.

Adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4) from Bacillus cereus NCIB 8122 has been purified to electrophoretic homogeneity by ammonium sulfate precipitation, gel filtration through Sephadex G-100, DEAE-Sephadex A-50 chromatography and ion-exchange HPLC on DEAE-Polyol. The enzyme activity is stabilized (at temperatures from 0 degrees C to 40 degrees C) by 50 mM NH4+ or K+, while it is irreversibly lost in the absence of these or a few other monovalent cations. Glycerol (24% by volume) helps the cation in stabilizing the enzyme activity above 40 degrees C, but also exerts per se a noticeable protecting effect at room temperature. B. cereus adenosine deaminase displays the following properties: Mr on Sephadex G-200, 68,000; Mr in SDS-polyacrylamide gel electrophoresis, 53,700; optimal pH-stability (in the presence of 50 mM KCl) over the range 8-11 at 4 degrees C, and maximal catalytic activity at 30 degrees C between pH 7 and 10; Km for adenosine around 50 microM over the same pH range and Km for 2'-deoxyadenosine around 400 microM.

Adenosine Deaminase↗
PubMed1986

Sites of cleavage of rabbit muscle aldolase by purified cathepsin M from rabbit liver.

Rabbit liver cathepsin M, a sulfhydryl proteinase similar in catalytic properties to cathepsin B, causes a decrease in the activity of rabbit muscle aldolase assayed with fructose 1,6-bisphosphate but not with fructose 1-phosphate. Proteolytic modification of aldolase by cathepsin M is limited to the removal of small peptides from the COOH-terminus, including the COOH-terminal hexapeptide NH2-Ile-Ser-Asn-His-Ala-TyrOH. Correlation of loss of aldolase activity with COOH-terminal modification indicates that only three of the four subunits of muscle aldolase contribute to the catalytic activity of the tetrameric enzyme.

Animals↗
PubMed1985

Purification and properties of rabbit liver cathepsin M and cathepsin B.

Cathepsins M and B from rabbit liver lysosomes were separated by chromatography on Ultrogel AcA34 at low ionic strength and purified to homogeneity, and their catalytic and molecular properties were compared. Cathepsin M was relatively inactive with synthetic peptide substrates. Thus, it hydrolyzed benzoyl arginine naphthylamide at only one-fifth the rate observed with cathepsin B, and no activity was detected with Gly-Phe naphthylamide which is a relatively good substrate for cathepsin B. On the other hand, cathepsin M exhibited a preference for protein substrates. It was more active than cathepsin B in catalyzing the inactivation of the following enzymes: rabbit muscle or liver fructose-1,6-bisphosphate aldolases, rabbit liver fructose-1,6-bisphosphatase and pyruvate kinase, yeast glucose-6-phosphate dehydrogenase, and rabbit muscle glyceraldehyde-3-phosphate dehydrogenase. With glucagon as substrate, both enzymes showed similar peptidyl dipeptidase activities with some minor differences in peptide bond specificity. Cathepsins M and B are similar in size, with apparent molecular weights of 30,200 for cathepsin M and 28,800 for cathepsin B, and in amino acid composition and carbohydrate content. Each contains approximately 2-3 equivalents/mol glucosamine, 3 equivalents/mol mannose, and no fucose or galactosamine. They also show similar microheterogeneity in sodium dodecylsulfate-gel electrophoresis and isoelectric focusing; this microheterogeneity is probably related to differences in glycosylation. Extensive homology in primary structure for the two proteins was indicated by the similar patterns of peptides formed on digestion with trypsin.

Amino Acids↗
PubMed1985

Purification and characterization of two leaf polypeptide inhibitors of leaf protease from alfalfa (Medicago sativa).

Two polypeptides with antiproteolytic activities have been isolated from alfalfa leaves. Polypeptide I resembles the previously described plant protease inhibitors in both structural and functional features; it has a molecular weight of 15,000, a random coil secondary structure, and inhibits exogenous protease as well as alfalfa leaf protease. Polypeptide II is a novel type of plant inhibitor with a molecular weight of 6300 and a highly organized structure with a high (40-50%) alpha-helix content. It only inhibits endogenous protease with a molar stoichiometry polypeptide/enzyme protein of 1.

Amino Acids↗
PubMed1978

pH controlled diazo coupling of aldolase. Selective formation of diazothioether chromophores and retention of enzyme activity.

pH Conditions have been found which achieve selective reaction of diazotized p-amino benzoate with cysteine residues of rabbit muscle aldolase. The difference in reactivity of the two sulphydryl groups involved, (Cys--237 and Cys--287) permits one to form either four or eight diazothioethers on the tetrameric enzyme and obtain a homogeneous protein. In both cases the enzyme became slightly more active in the fructose-1, 6-bisphosphate cleavage, the KM value being retained. The results have been discussed with regard to chemically modifying an enzyme to change its physical, chemical and immunological properties, whilst leaving the catalytical activity unmodified.

Animals↗
PubMed1977

Asymmetric hydrogenation of unsaturated peptides.

Eleven unsaturated peptides, containing one or two dehydro-phenylalanyl (dehydro-Phe) residues and a C-terminal L-amino acid have been hydrogenated in the presence of palladium-on-charcoal. Hydrolysis of the saturated peptides thus obtained gave optically active phenylalanine showing the occurrence of asymmetric induction during the hydrogenation. Both mono-unsaturated dipeptides and doubly unsaturated tripeptides with L-Glu, L-Leu and L-Val as chiral end-group afforded L-Phe in 40-50% optical yield. In the case of the tripeptide N-acetyl-(dehydro-Phe)-(dehydro-Tyr)-L-Glu the asymmetric induction was higher (70%) for the unsaturated residue which is farther from the chiral end-group along the peptide chain. The results are discussed on the bases of Prelog rule and the rigid dissymmetric conformation of the dehydropeptides in solution.

Amino Acids↗
PubMed1975

Catalytically active azoaldolase. Preparation on solid support.

A procedure for the coupling at pH 7.2 of p-carboxy benzene diazonium chloride with rabbit muscle aldolase supported on phosphocellulose is described and some of the spectroscopic, structural and catalytic features of the material obtained are reported. The tetrameric azoenzyme is homogeneous in disc gel electrophoresis even in the presence of 8 M urea. Twelve molecules of the reactant are bound to the protein. Eight azocysteins are identified by both spectroscopic studies and amino acid analysis. The presence of one azohistidine is suggested by the spectroscopic data along with the presence of other, as yet unknown, chromophores. The azoaldolase shows unchanged catalytic properties using both D-fructose 1,6-bisphosphate and D-fructose 1-phosphate as substrates, as compared with the native enzyme. The pH profile of the enzyme activity is broadened towards the alkaline region but no changes occur in the physiological range of pH.

Amino Acids↗
PubMedDate not supplied

Influence of experimental diabetes on brain levels of monoamine neurotransmitters and their precursor amino acids during tryptophan loading.

The variations in serum and brain concentrations of the large neutral amino acids and the simultaneous changes in brain levels of monoamine neurotransmitters have been studied in normal and streptozotocin-diabetic rats after tryptophan loading. An impaired acute accumulation of tryptophan and serotonin in the brain of diabetic rats was observed, concomitantly with a much faster disappearance of the administered tryptophan from the bloodstream in these animals than in controls. Following the tryptophan load, transient differences in the brain levels of catecholamine neurotransmitters became also apparent between the two groups of rats in correlation with differences in the brain uptake and levels of tyrosine. In diabetic animals, the basal brain concentrations of serotonin and dopamine were normal and those of norepinephrine were increased. Since uptake of the precursors tryptophan and tyrosine from the blood is chronically reduced, it is likely that long-term adjustments of neurotransmitter metabolism occur in the diabetic brain.

Amino Acids↗