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Preliminary experimental data on inhibition of beta-lactamase I from B. cereus by Cu (II) and Zn (II)
No full textDerivative spectroscopy as a nonperturbative tool to detect the state of liposome-entrapped sulbactam
No full textSulbactam, a β-lactam antibiotic, absorbs uv light at 273 nm when in alkaline media, whereas at neutral or acidic pH this peak disappears. Sulbactam-loaded liposomes, prepared by reverse-phase evaporation, were spectroscopically analyzed by the derivative mode measuring the peak-through amplitude between +258 and -285 nm, so that the spectral interference of the sample is eliminated. Taking advantage of this experimental approach, we could study the influence of different parameters on the dissociation state of the drug when entrapped in dipalmitoyl phosphatidylcholine liposomes. In particular, following the time course of sulbactam peak disappearance, we found that: (i) the effectiveness of protonating the sulbactam of the chosen buffers is acetate/acetic acid > succinate/succinic acid > citrate/citric acid; (ii) the rate of signal disappearance is influenced by the externally imposed pH and can be somewhat related to the dissociation state of the organic acids; (iii) as expected, the whole phenomenon is temperature dependent. The observations reported here might be the basis for quantitative permeation studies in synthetic and/or natural membranes using this methodology
Rapid characterization and partial purification of various animal amine oxidases
No full textThe use of chromatofocusing to obtain a rapid characterization of tissue amine oxidases from various mammals is proposed. This technique yields partially purified enzymes well suited for immunological studies. Chromatofocusing can be also used in a three-step purification of pig kidney diamine oxidase. © 1984 Birkhäuser Verlag
Proteolytic interconversion and N-terminal sequences of the Citrobacter diversus major β-lactamases
Full text linkThe N-terminal sequences of the two major β-lactamases produced by Citrobacter diversus differed only by the absence of the first residue in form II and the loss of five amino acid residues at the C-terminal end. Limited proteolysis of the homogeneous form I protein yielded a variety of enzymatically active products. In the major product obtained after the action of papain, the first three N-terminal residues of form I had been cleaved, whereas at the C-terminal end the treated enzyme lacked five residues. However, this cannot explain the different behaviours of form I, form II and papain digestion product upon chromatofocusing. Form I, which was sequenced up to position 56, exhibited a very high degree of similarity with a Klebsiella oxytoca β-lactamase. The determined sequence, which contained the active serine residue, demonstrated that the chromosome-encoded β-lactamase of Citrobacter diversus belong to class A
Chromosome-encoded β-lactamases of Citrobacter diversus. Interaction with β-iodopenicillanate and labelling of the active site
No full textBoth forms of the chromosome-encoded β-lactamase of Citrobacter diversus react with β-iodopenicillanate at a rate characteristic of of class A β-lactamases. The active site of form I was labelled with the same reagent. The sequence of the peptide obtained after trypsin hydrolysis is identical with that of a peptide obtained in a similar manner from the chromosome-encoded β-lactamase of Klebsiella pneumoniae
On the kinetic interaction between ceftriaxone and some β-lactamases
No full textThe activity of β-lactamases from Citrobacter diversus ULA-27 on ceftriaxone, a widely recognized third-generation cephalosporin, has been examined and compared to the activity of various other β-lactamases from different sources. Ceftriaxone (Roche S.p.A. Milan) was found to be resistant to hydrolysis by β-lactamases from Enterobacter cloacae and Bacillus cereus, but susceptible to β-lactamases from Mycobacterium fortuitum strain Cow 18 and, mostly, to β-lactamases from various strains of Citrobacter diversus. Derivatives with substituents in the 3-position of ceftriaxone, namely cefotaxime (Roussel Maestretti S.p.A., Milan) and ceftizoxime (Farmitalia Carlo Erba, Milan), were much less susceptible to hydrolysis by C. diversus ULA-27 enzymes (22 and 6% of ceftriaxone hydrolysis, respectively), the hydrolysis rate being paralleled by differences in MIC values. Ceftriaxone inhibited the activity of E. cloacae β-lactamases toward cefazolin as substrate, but the inhibition was totally abolished by preincubation of ceftriaxone with the enzyme before addition of the substrate. Overall, the data point to a relevance of C. diversus ULA-27 β-lactamases in the mechanism of resistance of this strain to the various third-generation cephalosporins
Broad spectrum β-lactamases of citrobacter diversus
No full textCitrobacter diversus NF85 produced a chromosomal β-lactamase that was induced by a variety of β-lactam antibiotics. Two major forms of the enzyme, with isoelectric points (pI's) of 5·7 and 6·2, were found in crude cell extracts. Derepressed mutants of NF85, generated by nitrosoguanidine treatment, displayed different levels of β-lactamase expression to the parent strain and had different patterns of resistance to a range of β-lactam antibiotics. Those mutants of NF85 that were totally derepressed, expressing high, constitutive levels of enzyme, were found to have an additional β-lactamase activity with a pI of 6·8. © 1990 by The British Society for Antimicrobial Chemotherapy
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