Search PubMed⌕ Search

Biomedical subjects

G Cercignani

Publications and source records attributed to G Cercignani.

At least 37 records · Page 2Linked to original sources
PubMed1989

A fluorescence study of substrate and inhibitor binding to bovine liver dihydrofolate reductase.

1. Covalent coupling of fluorescein to methotrexate (MTX) by a 5-carbon spacer yields a dihydrofolate reductase (DHFR) inhibitor (FMTX) with Ki = 11 nM. 2. FMTX shows a fluorescence quenching with respect to fluorescein which is relieved by binding to the enzyme. 3. The dissociation constants (Kd) of MTX, FMTX, NADPH and 7,8-dihydrofolate (DHF) from bovine liver DHFR have been determined by fluorometric titrations. 4. The Kd values for NADPH, MTX and FMTX from the complementary binary complexes (MTX.DHFR, FMTX.DHFR and NADPH.DHFR) were also obtained; these show a 2- to 4-fold decrease with respect to those obtained by titration of the free enzyme. 5. A competitive assay for MTX has been developed by exploiting the fluorescence enhancement of DHFR-bound FMTX. This assay may be useful for the routine determination of MTX in the concentration range from 10(-9) to 10(-7) M.

Animals↗
PubMed1987

The pH dependence of spectral parameters for Kalckar's adenosine deaminase assay.

Optimal monitor wavelengths and differential millimolar extinction coefficients (m delta epsilon) for rate determination of reactions catalyzed by adenosine deaminases on several substrates have been investigated as a function of pH in the range from 6.5 to 12. The values found are in some cases at variance with those quoted in the biochemical literature. The effect of pH on m delta epsilon values is shown to be clearly related to acid-base properties of product and/or substrate in the reaction. Experimental data are in most cases used to derive analytical functions describing the pH dependence of m delta epsilon. For the conversion of adenosine to inosine at pH 6.5, the following values of m delta epsilon +/- SE were obtained: at 263 nm, 8.27 +/- 0.02; at 264 nm, 8.36 +/- 0.02; at 265 nm, 8.27 +/- 0.03. These represent absolute maximal values as a function of pH.

Adenosine↗
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↗
PubMed1979

[Enzymologic characterization of adenosine nucleosidase of medicinal plants (Medicago sativa)].

Adenosine nucleosidase (adenosine ribohydrolase, E C 3.2.2.7) was purified from alfalfa leaf juice. The final preparation shows a single band on polyacrylamide gel electrophoresis; the enzyme activity is stable for 12 hrs between pH 5.5 and pH 8.5, but is completely lost on heating at 55 degrees C for 10 min. Optimal pH for the hydrolysis of adenosine is between pH 5 and pH 6. Among nine purine nucleosides tested, only adenosine, 2'-deoxyadenosine and purine riboside were hydrolyzed by the enzyme preparation. A Km value of 7 x 10(-6) M was found with adenosine as substrate at pH 7.4. Of the two reaction products, adenine exerted a weak inhibitory effect, while D-ribose was without effect on the initial rate of adenosine hydrolysis. The data reported are compared with those obtained on the enzymes from other plant sources.

Adenosine↗
PubMed1976

Evaluation of the genetic effects induced by vinyl chloride monomer (VCM) under mammalian metabolic activation: studies in vitro and in vivo.

As part of a programme of investigations on the biological effects of the industrial compound vinyl chloride monomer (VCM), the raw material for the production of polyvinyl chloride (PVC), analyses on the genetic effects by this compound have been done by experiments (in vitro) which have taken mammalian metabolism into account. Vinyl chloride in the presence of purified microsomes (sedimented at 105,000 g) obtained from mouse liver was converted into an active metabolite(s) which produced gene mutations in the yeast Schizosaccharomyces pombe (forward mutation) and gene conversions in two loci of a diploid Saccharomyces cerevisiae. Moreover, the compound was active in the host-mediated assay, when mice were treated with an oral dose of 700 mg/kg. The role is discussed of mutagenicity tests for the prediction of both genetic and carcinogenic risks of chemical compounds in industrial use.

Animals↗