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R Scandurra

Publications and source records attributed to R Scandurra.

At least 55 records · Page 3Linked to original sources
PubMed1981

[Methods of determination of vitamin B 12].

A brief review on the methods for vitamin B12 determination is presented. The most appropriate utilization of each method based on its sensitivity, on the availability of the sample and on practical difficulties has been indicated. The methods have been divided into: a) physico-chemical methods, where the vitamin is identified spectrophotometrically; b) microbiological methods, where the vitamin is determined quantitatively by means of the growth of cobalamine dependent bacterial strains; c) kinetic methods, based on the different rate of conversion of the different cobalamines into dicyanocobalamine in the presence of an alkaline solution of cyanide; d) enzymatic methods, where activation of apodioldehydrase is used for the quantitative determination of adenosylcobalamine; e) chromatographic methods, where the separation of the cobalamines is obtained by chromatography and the quantitative determination is obtained by means of the growth of cobalamine-dependent bacterial strains (bioautography); f) radioisotopic methods where total cobalamines are determined quantitatively by measuring radioactivity after addition of (57Co)-CNCbl and a specific binder.

Chromatography↗
PubMed1977

[Copper and nervous system. An experimental study (author's transl)].

Sodium azide is known to produce alterations in mammalian copper proteins, thus rendering them unable to bind exogenous metal, which remains in the "labile pool" condition. Continuous administration of sodium azide at LD50 for 30 days causes copper accumulation in several tissues and even in the nervous system, with characteristic changes in neurones and glial cells, very much resembling the alterations observed in Wilson's disease. Dietary copper administration, on the contrary, though raising the level of tissue-bound metal, does not produce cellular damage. These findings allow us to suppose that sodium azide may alterate the coppper chelating proteins in the tissues, especially in the nervous system, thus causing the storage of cell-toxic "labile pool" metal. The pathogenesis of Wilson's disease and the problem of "pathoclisis" in the nervous system are debated.

Animals↗
PubMed1976

Chemical modifications of histidine residues in cytoplasmic asparate aminotransferase from beef kidney.

Holo and apoenzyme of aspartate aminotransferase from beef kidney are 80% inactivated by photoxidation in the presence of 2 X 10(-6) M tetraiodofluroescein with the modification of two histidine residues per enzyme protomer. At a higher concentration (1 X 10(-5) M) a tyrosine residue is also modified. The keto substrates, ketoglutarate and oxalacetate, protect the enzyme from photoxidation. Diethylpyrocarbonate modifies three histidine residues per enzyme protomer and reduces the activity only 10%. These results suggest that the two histidine residues photoxidized through the sensitizer, are located in the active site of the enzyme, at least one of these appears to be involved in ketosubstrate binding. The other three histidines modified by diethylpyrocarbonate are likely located on the enzyme surface and are not involved in the catalytic activity of the enzyme.

Animals↗
PubMed1976

Role of tyrosine residues in cytoplasmic aspartate aminotransferase from beef kidney.

Cytoplasmic aspartate aminotransferase from beef kidney loses 25% of its activity on nitration with tetranitromethane while the apoenzyme about 95%. In the holoenzyme 0.5 tyrosine residue and 1.0 tyrosine residue in the apoenzyme are nitrated per enzyme protomer. In addition 1 cysteine residue per protomer is oxidized in both. The presence of substrates, alpha-ketoglutarate and glutamate, both at ten times their Km values, does not change these results. Mercaptoethanol does not affect the residual activity of either the nitrated holo or apoenzyme. Dithionite abolishes the activity of the nitrated holoenzyme by reducing tha coenzyme moiety. It has no effect on the native holoenzyme or on either the native or nitroapoenzyme.

Animals↗
PubMed1976

The phosphopyridoxyl peptide from the mitochondrial aspartate aminotransferase of beef kidney.

The sequence around the coenzyme-binding lysine of mitochondrial aspartate amino-transferase from beef kidney was determined. The holoenzyme was treated with NaB3H4 and digested with thermolysin; the labelled peptide was isolated and its sequence proved to be identical with sequences around the coenzyme site from the same isoenzyme of different organs and animals (pig heart and sheep liver). The sequences of the phosphopyridoxyl peptides of the mitochondrial aspartate aminotransferases appear to be closely related to the corresponding peptides from the cytoplasmic isoenzymes.

Amino Acids↗
PubMed1976

Simultaneous purification of mitochondrial and cytoplasmic isozymes of aspartate aminotransferase from beef kidney.

Mitochondrial and cytoplasmic isozymes of aspartate transaminase are separated from beef kidney homogenates by ammonium sulfate fractionation. The mitochondrial isozyme is purified essentially as described earlier (Eur. J. Biochem., 1972, 26, 196-206) with slight modification in order to increase the yield. The cytoplasmic isozyme is purified by heat treatment followed by ion exchange cellulose chromatography and gel chromatography. The enzyme is pure in the ultracentrifuge and in polyacrylamide gel electrophoresis; it shows only one anionic band and no subforms. It has a molecular weight of 93,000 +/- 2000 and is composed of two subunits of 46,000 M.W. The enzyme has a specific activity of 49 micronmoles of oxalacetate x min-1 x mg-1. It contains 5 SH groups per subunit; three are directly titratable with p-mercuribenzoate and the other two only after addition of 0.2% SDS; there is no evidence of S-S groups. Km values for aspartate, glutamate, alpha-ketoglutarate and oxalacetate are in the order 1.25, 3.2, 0.06 and 0.41 mM in the cytoplasmic isozyme and 0.7, 5.0, 1.25 and 0.12 mM in the mitochondrial one.

Amino Acids↗
PubMed1975

Role of tyrosine residues in mitochondrial aspartate aminotransferase from beef kidney.

Mitochondrial aspartate aminotransferase from beef kidney is 50% inhibited after 2 hr treatment with 2.5 mM tetranitromethane at pH 8. Two tyrosine residues per enzyme protomer (46,000 daltons) are modified by the reagent either in the holoenzyme or in the apoenzyme. In both cases the five SH groups titratable with p-mercuribenzoate are not modified by the reagent. However, with a tetranitromethane concentration higher than 2.5 mM and 10 mM mercaptoethanol, an additional tyrosine residue is nitrated in both holo- and apoenzymes. These results are not affected by the presence in the incubation mixture of the substrates alpha-ketoglutarate and glutamate both at ten times their Km values. Mercaptoethanol does not impair the recombination of native or nitrated apoenzyme with the coenzyme and does not reduce the coenzyme moiety of native or nitrated holoenzyme, but promotes a conformational change in the nitrated holoenzyme which causes inactivation. Hydrosulfite promotes the reduction of the coenzyme moiety of native and nitro holoenzyme resulting in their inactivation, largely in the nitrated form. The recombination of the coenzyme with native or nitrated apoenzyme is not influenced by hydrosulfite.

Animals↗
PubMed1975

Role of tryptophan, histidine and methionine residues in the catalytic activity of mitochondrial aspartate aminotransferase from beef kidney.

The role of tryptophan, methionine, and histidine residues in mitochondrial aspartate aminotransferase from beef kidney has been established by using N-bromosuccinimide, 2-hydroxy-5-nitrobenzylbromide, and tetraiodofluoresceine as specific chemical modifiers of the amino acid residues of the enzyme. Since N-bromosuccinimide promotes extensive inactivation of the enzyme and the chemical modification of 1.65 tryptophan and 3 methionine residues per enzymes protomer, 2-hydroxy-5-nitrobenzylbromide modifies once more 1.65 tryptophan residues per enzyme protomer but induces only 10% inactivation of the enzyme. Tetraiodofluoresceine exerts a 40% inactivation of the enzyme which is due to the chemical modification of 5.8 histidine res in

Animals↗