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L Politi

Publications and source records attributed to L Politi.

48 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↗
PubMed1980

[Surgical treatment of postinfarctual left ventricular aneurysm (author's transl)].

Ventricular aneurysm is a frequent complication of myocardial infarction, but its diagnostic and prognostic implications are not fully defined. A surgical series of 66 ventricular resections for symptomatic left ventricular aneurysm is analyzed. Pts. age varied between 26-29 years; the interval between the episode of infarction and operation from 2 mos. to 12 years. Indication for surgery was angina in 53% of the cases, heart failure in 23%, arrhythmias in 15%, angina and failure in 9%. In 55 cases surgical findings were consistent with true aneurysm in the anatomical sense, in 11 cases with a wide area of wall akinesia. In 24 cases endocavitary thrombosis was present. In 23 cases aneurysmectomy was the only surgical procedure, with closure of acquired VSD in 1 case and mitral valve prosthesis in 2 cases. In 43 cases aorto-coronary bypass grafting was associated (single bypass in 18, double in 23, triple in 2). Operative technique underwent modifications in time, in relation to the use of local and general hypothermia, of cardioplegia, of early aortic cross-clamping. Surgical mortality was of 7.5% (5 cases); the actuarial courve, including operative mortality, showed survival of 88% at 1 year and of 78% at 5 years interval. Correlation between mortality and clinical symptomatology, hemodynamic data and surgical findings was not statistically significant; a statistically highly significant correlation was found between mortality and operative technique. The results are interpreted and discussed in relation to the diagnostic definition of the problem, to the criteria of indication to surgery and to the operative technique.

Adult↗
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

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↗
PubMedDate not supplied

[Imaging of bronchogenic cysts].

Bronchogenic cysts, unlike the other mediastinal cysts, exhibit a high incidence of complications, which makes their resection advisable even if no symptoms are present. The correct diagnosis should thus be made with the available imaging modalities. We reviewed our series of 11 bronchogenic cysts, all of them studied with conventional radiology (CR), as well as with such newer imaging modalities as CT and/or MRI. All mediastinal lesions had fluid density at CT and were homogeneously hyperintense on T2-weighted MR images. On the contrary, on T1-weighted images, some lesions were hypointense and some hyperintense, probably because of their rich protein content. In contrast, hilar or pulmonary lesions had air inside, except for one case--characterized by multiple localizations--in which the hilar lesion exhibited the same fluid density as the mediastinal lesions. The CT or MR finding of a lesion with fluid content below the carina permits a nearly unquestionable diagnosis of bronchogenic cyst since the other cystic lesions involve this region very rarely. In all the other cases, other types of mediastinal or hilar-pulmonary lesions cannot be ruled out. In particular, in case of cysts in paraesophageal site, no imaging modality permits to differentiate bronchogenic from enteric cysts; in some cases, the differential diagnosis may be impossible even with histology of the resected specimen.

Adolescent↗