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M Nieto

Publications and source records attributed to M Nieto.

At least 91 records · Page 5Linked to original sources
PubMed1973

DD-carboxypeptidase-transpeptidase and killing site of beta-lactam antibiotics in Streptomyces strains R39, R61, and K11.

Additional evidence is given that in Streptomyces strains R39, R61, and K11 the same enzyme performs dd-carboxypeptidase and transpeptidase activities and that this enzyme is the killing site of beta-lactam antibiotics. With strain R61, it was found that the exocellular enzyme has a sensitivity towards some antibiotics different from that of the membrane-bound enzyme. Under the growth conditions used in the present investigations, beta-lactamase activity was not involved in susceptibility to beta-lactam antibiotics.

Acyltransferases↗
PubMed1972

Reversal by a specific peptide (diacetyl-alpha gamma-L-diaminobutyryl-D-alanyl-D-alanine) of vancomycin inhibition in intact bacteria and cell-free preparations.

Vancomycin inhibited the growth of Bacillus megaterium, Staphylococcus aureus and Micrococcus lysodeikticus, and in cell-free preparations from B. megaterium it inhibited the formation of mucopeptide and enhanced the accumulation of the lipid intermediate in the biosynthetic pathway. All these inhibitory processes were reversed by the presence of a synthetic peptide analogous to un-cross-linked mucopeptide side chains, namely diacetyl-l-diaminobutyryl-d-alanyl-d-alanine. A considerable amount of vancomycin was found in recovering cells, whether recovery was caused by peptide or took place naturally because a low initial concentration of antibiotic was used. In cell-free preparations pretreated with vancomycin, continued inhibition of mucopeptide synthesis depended on the presence of cell-wall material. This inhibition was also reversible by added peptide.

Alanine↗
PubMed1972

Transpeptidase activity of Streptomyces D-alanyl-D carboxypeptidases.

In the presence of N(alpha),N(epsilon)-diacetyl-L-Lys-D-Ala-D-Ala as donor, and either D-[(14)C]alanine, [(14)C]-glycine, or meso-[(3)H]diaminopimelic acid as acceptor, the DD carboxypeptidases from Streptomyces R61 and R39 catalyze a transpeptidation reaction with the release of terminal D-alanine from the donor and the formation of either N(alpha),N(epsilon)-diacetyl-L-Lys-D-Ala-D-[(14)C]Ala, N(alpha),N(epsilon)-diacetyl-L-Lys-D-Ala-[(14)C] Gly, or N(alpha),N(epsilon)-diacetyl-L-Lys-D-Ala-D-meso- [(3)H]diaminopimelic acid. The reaction appears to be a true transpeptidation, and is not simply a "reversal of hydrolysis". Transpeptidation is inhibited by pencillin at concentrations that inhibit hydrolysis (carboxypeptidase action) of the donor peptide. There are differences in the specificity profiles of the Streptomyces enzymes for acceptor molecules:only the R61 enzyme used [(14)C]Gly-Gly as acceptor; transfer of N(alpha),N(epsilon)-diacetyl-L-Lys-D-Ala to this acceptor resulted in the formation of N(alpha),N(epsilon)-diacetyl-Lys-D-Ala-[(14)C] Gly-Gly, with the synthesis of a (D-Ala-Gly) peptide bond in an endoposition.

Alanine↗
PubMed1971

Physicochemical properties of vancomycin and iodovancomycin and their complexes with diacetyl-L-lysyl-D-alanyl-D-alanine.

Electrometric and spectrophotometric titrations showed vancomycin to contain groups having pK values of about 2.9, 7.2, 8.6, 9.6, 10.5 and 11.7. Of these the four last-named were phenolic. Titration above pH11 and below pH1 was irreversible and antibiotic potency was destroyed. Combination with the specific peptide diacetyl-l-lysyl-d-alanyl-d-alanine hindered the titration of the first three phenolic groups. Spectrophotometric titration of iodovancomycin showed that the phenolic group with pK 9.6 was the one iodinated. The stability of the vancomycin-peptide complex in the range pH1-13 showed that complex-formation occurred only when carboxyl groups were ionized and the phenolic groups were non-ionized. The complex was formed in concentrations of urea up to 8m, of potassium chloride up to 4m, of sodium dodecyl sulphate up to 1%, and at temperatures up to 60 degrees C. From titration curves, organic chlorine and iodine analysis, and combination with peptide, a minimum molecular weight for vancomycin of 1700-1800 was estimated. Optical-rotatory-dispersion and circular-dichroism experiments suggested that vancomycin has only limited conformational flexibility. Both vancomycin and its complexes with peptide exhibited properties suggesting aggregation. Vancomycin and iodovancomycin can be fractionated into a main fraction and at least three minor components. The isolation of these fractions salt-free is described and their antibiotic properties are shown to correlate with their ability to form complexes with peptide.

Alanine↗
PubMed1971

Modifications of the acyl-D-alanyl-D-alanine terminus affecting complex-formation with vancomycin.

Vancomycin forms complexes with peptides terminating in d-alanyl-d-alanine that are analogous to the biosynthetic precursors of bacterial mucopeptides. The specificity of complex-formation has been studied by means of many synthetic peptides, prepared by both solid-phase and conventional methods. The following conclusions can be drawn: (a) three amide linkages are required to form a stable complex; (b) the terminal carboxyl group must be free; (c) the carboxyl terminal and subterminal residues must be either glycine or of the d-configuration; (d) the size of the side chain in these residues greatly influences the affinity for vancomycin, a methyl group being the optimum in each case; (e) the nature of the side chain in the third and fourth residues has a smaller effect on complex-formation, but an l-configuration was somewhat better than a d-configuration in the third position. In addition to acyl-d-alanyl-d-alanine, other peptides that occur in bacterial cell walls will combine with vancomycin, although less strongly, e.g. acyl-d-alanyl-d-alpha-amino acid (where the terminal d-residue may form the cross-link in mucopeptide structure) and acyl-l-alanyl-d-glutamylglycine (a sequence found in the mucopeptide of Micrococcus lysodeikticus and related organisms). These results throw some light on the specificity of the uptake of vancomycin by living bacteria.

Alanine↗
PubMed1971

The specificity of combination between ristocetins and peptides related to bacterial cell wall mucopeptide precursors.

The affinity of ristocetin B for analogues of the C-terminal tripeptide sequence of bacterial cell wall mucopeptide precursors resembles that of vancomycin. Complex-formation requires a d-configuration in the two amino acid residues of the C-terminal dipeptide, an l-configuration is preferred in the preceding amino acid residue and positive charges on the peptide molecule decrease its affinity. The specificity of ristocetin B, however, differs from that of vancomycin in the requirements for the size of the side chains on the C-terminal dipeptide. These differences may explain the observed differences in antibiotic behaviour of vancomycin and ristocetin with particular micro-organisms. The optical rotatory dispersion and u.v.-absorption characteristics of the ristocetins are very different from those of vancomycin but nearly identical with those of ristomycin A. Aglycones prepared from ristomycin A were antibiotically active and also combined with a specific peptide.

Amino Acid Sequence↗
PubMed1970

The preparation of iodinated vancomycin and its distribution in bacteria treated with the antibiotic.

Vancomycin was radioactively labelled by iodination with (125)I.Iodinated vancomycin was only a little less potent as an antibiotic than vancomycin itself. It was shown, both by chromatography and differential absorption measurements, to combine with acyl-d-alanyl-d-alanine residues. Radioactive vancomycin was used to follow the fate of the antibiotic in bacteria that had been subjected to the least concentration required to inhibit growth. Most of the radioactivity was in the cell walls, although some was found in the membrane fraction. The latter proportion increased during longer incubations with the antibiotic. Pre-formed protoplasts adsorbed very little vancomycin. Mg(2+) removed labelled vancomycin from the mucopeptide of Bacillus licheniformis, but had little effect on the antibiotic adsorbed on Micrococcus lysodeikticus, either in vivo or on previously isolated cell walls. Specific peptide was shown to compete with cell walls for vancomycin and it also extracted from cell-wall samples the labelled compound that had been adsorbed on M. lysodeikticus living cells.

Adsorption↗
PubMedDate not supplied

[Alkaloids of the Annonaceae: composition of the bark of the trunk and roots of Enantia pilosa].

The alkaloidal content of stem- and root-bark of Enantia pilosa Exell (Annonaceae) was studied and compared to that of other Enantia spp. Six aporphine alkaloids were isolated; two alkaloids, oliverine and oliveridine, were found in major amounts; two oxoaporphines, liriodenine and lanuginosine, were present; two other alkaloids, N-oxyoliverine and N-oxyoliveridine, were isolated for the first time. Quaternary alkaloids from stem-bark are presently under investigation.

Aporphines↗
PubMedDate not supplied

[Immunological study in patients with severe myoclonic epilepsy in childhood].

OBJECTIVE: Clinical and experimental data support the role of immune mechanisms in the pathogeny of childhood epilepsy. The purpose of this report is to study the immunological aspects in severe myoclonic epilepsy in infancy (SMEI). PATIENTS AND METHODS: 12 patients selected according to the following criteria: no previous personal history of disease, frequent familial history of epilepsy, beginning in the first year of life with seizures usually febriles, onset of afebrile seizures between 18 months and 4 years, normal EEG and psychomotor development are at the onset, seizures resistant to antiepileptic drugs. The following immunological evaluation, has been carried out: granulocytes phagocytic activity, lymphocytics subpopulations, serum immunoglobulins and IgG subclasses, hemolytic capacity of complement, lymphocytic transformation test. RESULTS: In five cases the immunological study was normal; five cases had IgA deficiency, associated in two to high serum IgG1 levels and in two to high IgG1 and low IgG2 levels; one case shows an IgM increase associated to hemolytic capacity of complement deficiency (CH50); four cases have a reduced response to different mitogens. CONCLUSIONS: The value of this results is doubtful. It is possible that genetical and environmental factors are involved in SMEI and that the immunological abnormalities found favor the hyperergic reactions in given circumstances.

Adolescent↗