1,721,175 research outputs found
Chimica e biochimica per le lauree triennali dell'area biomedica
No full textPrefazione
Questo libro origina dal “Corso di Biochimica per le Lauree Triennali di Area Sanitaria” edito da Piccin. Come il precedente, anche questo è destinato agli Studenti che affrontano lo studio della Biochimica per la maggior parte delle Lauree Triennali di Area Biomedica. Pur restando un cardine insostituibile della formazione del nuovo laureato, l’insegnamento della Biochimica si è tuttavia evoluto rispetto a quando vide la luce la prima edizione del “Corso”. Per esempio, in numerosi ordinamenti didattici delle Lauree Triennali il corso di Biochimica è stato ampliato ed ora spesso comprende anche quello di Chimica. Per questo motivo, abbiamo voluto aggiungere due capitoli dedicati esclusivamente alla Chimica, che possa-no servire come Chimica e Propedeutica Biochimica. Ma confidiamo che lo sforzo effettuato per sintetiz-zare in maniera comprensibile una materia vasta come la Chimica serva anche come semplice punto di appoggio per quelle nozioni di Biochimica che facevano affidamento su conoscenze di Chimica talora mancanti. Questa scelta è stata supportata dall’osservazione che spesso gli studenti che affrontavano il corso di Biochimica affidandosi al precedente libro erano in difficoltà quando si davano per scontate del-le nozioni che, evidentemente, tanto scontate non erano.
Oltre alla Chimica, la presente edizione prevede anche, rispetto alla versione precedente, lo sviluppo delle nozioni di base riguardanti il meccanismo di replicazione del DNA e la sua traduzione in proteine che, mentre per alcuni ordinamenti è appannaggio dei corsi di Biologia, per altri è invece trattato in quelli di Bio-chimica. Ovviamente non si sono trattati alcuni argomenti-chiave di estrema importanza riguardanti i dog-mi centrali della Biologia, della Biologia Molecolare e della Genetica, ma ci siamo limitati ad accennare a questi argomenti in maniera molto superficiale, lasciando ad altri eccellenti testi il compito di trattare più approfonditamente questi argomenti.
Le aggiunte accennate hanno forzato una certa ridistribuzione del materiale pre-esistente per facilitare l’unità discorsiva, ridurre le ripetizioni ed evitare accavallamenti. Si è preso spunto da questa necessità per snellire alcuni argomenti precedentemente trattati in maniera forse troppo approfondita ed approfondirne altri, sulla base di suggerimenti ed indicazioni pervenuti da numerosi Colleghi che desideriamo ringraziare.
Infine, altra novità di rilievo, si è introdotto l’uso dei colori. Riteniamo infatti che i colori siano impre-scindibili nell’apprendimento scorrevole di Chimica e Biochimica in quanto facilitano enormemente la com-prensione di concetti spesso ostici.
La presente edizione non vede modificato il layout delle edizioni precedenti, che ha incontrato il favore di studenti e docenti. Tale layout prevede un “sottotitolo” a molti dei paragrafi per facilitare il rapido in-quadramento degli argomenti trattati all’interno del capitolo stesso. Inoltre sono stati aggiunti degli appro-fondimenti a vari argomenti (in corpo più piccolo rispetto al resto del testo).
Il nostro sforzo ha tentato di dare una risposta all’esigenza, da parte di Studenti e Docenti, di un testo di Biochimica mirato al curriculum formativo delle Lauree Triennali. Ci abbiamo provato con un testo che ci auguriamo semplice senza essere superficiale, dettagliato senza essere ridondante, moderno senza essere speculativo, tradizionale senza essere sorpassato, cercando di rendere leggera la lettura e agevole lo studio senza scadere nella banalità. Ci auguriamo vivamente che anche questo testo possa essere di soddisfazione per Studenti e Docenti, ed invitiamo tutti a segnalarci errori ed omissioni.
MICHELE SAMAJA
RITA PARONI
Docenti di Chimica e Biochimica
Università degli Studi di Milan
Quantification of gentamicin in Mueller-Hinton agar by high-performance liquid chromatography
No full textThe aim of this study was to optimise a method for gentamicin determination in an agar matrix and to investigate if and how agar composition can affect the gentamicin diffusion kinetics during the agar diffusion tests for antibiotics sensitivity. Gentamicin was separated by RP-HPLC and detected at 365 nm after pre-column derivatization with 1-fluoro-2,4-dinitrobenzene. Recovery (> or = 79%), linearity (r2 > or = 0.997) and sensitivity (1 microg/ml) were assessed using four different agar matrices. The kinetics of gentamicin diffusion tested on BioMerieux and DID manufacturers' products showed in uninoculated agar plates significant differences that were even more pronounced in the presence of Pseudomonas aeruginosa metabolism
NO DOCUMENTABLE ROLE FOR XANTHINE-OXIDASE IN THE PATHOGENESIS OF HEPATIC IN-VIVO ISCHAEMIA/REPERFUSION INJURY
Full text linkAn investigation was made into the possible involvement of the enzyme xanthine oxidase (XO) (EC 1.1.3.22), both reversible (XOrev) and irreversible (XOirr), in damage observed after short-term in vivo hepatic ischaemia/reperfusion (60 or 120 min I and 15 min R) in fasted rats with: (i) a physiological content of XO (25%); and (ii) higher XO percentage (45%). In the latter the hepatic XO physiological percentage was increased by diethylmaleate treatment (300 mg kg(-1)) that depleted the cytosolic glutathione (GSH) to 14% of the controls. It was shown that, in animals with physiological content of XO, 60 and 120 min of hepatic ischaemia followed by 15 min reperfusion results in decreased GSH levels, and significantly increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) serum levels, without any modification of either the percentages of XO (XOirr and XOrev) or the hepatic thiobarbituric acid reactive substances (TBARS). Sixty minutes of ischaemia/reperfusion in rats with the higher XO level and lower hepatic GSH content led to further conversion of XDH to XOrev, with no increase in XOirr. In addition, the ALT and AST serum levels in these animals rose to the same extent as in normal rats after 120 min ischaemia and 15 min reperfusion, this extent being observed to be associated with a moderate increase in thiobarbituric acid reactive substances (TBARS). However, the administration of allopurinol, at a dose of 50 mg kg(-1), which almost completely inhibits XO activity, did not lead to any decrease in liver damage or TBARS. These findings exclude any role of XO in liver damage in the short term following ischaemia/reperfusion events, also when marked GSH depletion could increase the enzymatic physiological XO level
On thin coated plates with residual stress for the implementation of a crystalline undulator
No full textRecent experimental studies have indicated the feasibility of a crystalline undulator
obtained by depositing narrow periodic strips of silicon nitride on a silicon monocrystalline substrate.
The residual stress associated to the deposition of silicon nitride induces a micro-undulation in the
underlying silicon crystal. The periodicity and amplitude of the silicon crystal can be tuned to
reach a high efficiency of channeling of relativistic charged particles in the ordered structure of its
lattice. This communication reports on an ongoing research aimed at the mechanical modeling of
the undulator structure and the characterization of the constitutive properties of the materials
EFFECT OF GLUTATHIONE DEPLETION ON THE CONVERSION OF XANTHINE DEHYDROGENASE TO OXIDASE IN RAT-LIVER
No full textThe ability of endogenous glutathione (GSH) to modify the activity of the enzyme xanthine oxidase (XO) in rat liver was investigated. The effect of hepatic GSH depletion on the conversion of xanthine dehydrogenase (XDH) (EC 1.1.1.204) to XO (EC 1.1.3.22) was determined 10 min after i.p. administration of different amounts of diethylmaleate to fasted rats. After administration of 400 mg/kg, total hepatic non-protein GSH (reduced + oxidized GSH) decreased significantly to 14% of controls. In this condition the level of oxidized GSH was unchanged and no lipid peroxidation was observed, while a significant increase of reversible XO and a minor increase of the irreversible form of the enzyme was detected
Validation of methyl malondialdehyde as internal standard for malondialdehyde detection by capillary electrophoresis
No full textThe aim of this study was to validate, by capillary electrophoresis, the use of synthesized methyl malondialdehyde as the internal standard for the direct quantification of free and total (free+bound) malondialdehyde in biological samples. All analyses were performed in 20 cm x 50 microm uncoated capillaries at 20 degrees C, using 25 mmol/L borax (pH 9.3) and 5 mmol/L tetradecyltrimethylammonium bromide as running buffer. The applied voltage was -4kV (about 8 microA), the detector being set at 260 nm for a total run time of 8 min per sample. Free malondialdehyde was evaluated after acetonitrile extraction, while the samples evaluated for total malondialdehyde were, before extraction, hydrolyzed for 1h at 60 degrees C in the presence of 1 mol/L NaOH. The detection threshold was 0.2 micromol/L in microsomes and 0.4 micromol/L in plasma. As an application of the method, three pools of rat liver microsomes were quantified before (0.35+/-0.1 and 1.1+/-0.5 nmol/mg protein, free and total malondialdehyde, respectively, mean+/-SD) and after lipoperoxidation induction using systems able to generate oxygen free radicals (18.4+/-3.2 and 19.7+/-2.0 nmol/mg protein). The results were confirmed by isotopic dilution gas chromatography-mass spectrometry, used as the reference method. The feasibility of capillary electrophoresis for malondialdehyde determination in normal and pathological human plasma was also investigated
Semiquantitative discovery of ceramides by isoenergetic precursor ion scan in the triple quadrupole mass spectrometer: fundamental issues and proof-of-principle application
No full textThe triple quadrupole mass spectrometer (TSQ) has boosted discovery and quantification of trace components in biological samples using class-selective scan modes. The use of suitable molecular precursors and of characteristic fragment ions allows identifying and measuring ceramides with micro-heterogeneous fatty acid or sphingosine. Collision energy in the TSQ is a key parameter to extract information from MS-MS experiments for compounds of which authentic standards are not available.
We describe the theoretical basis and proof-of-principle application of a novel scan mode of a commercial TSQ by which the molecular precursor ions of all ceramides in a sample experiment the same Center-of-Mass Collision Energy (CoM-CE), irrespective of their different m/z values over a range of homologous or chemical analogs. At this value of CoM-CE, the different precursor ions have, for the same fragmentation channel, essentially the same fragment ion cross section, thus the same response factor for quantification. This scan mode can be applied to Precursor and Neutral Loss scans, and is performed by modulating the voltage drop of a scanning mass filter according to a specific linear function of precursor ion mass. Under this instrumental condition, all precursor ions collide under the same conditions and fragment to a common charged (in Precursor Ion scan) or neutral (in Neutral Loss scan) sub-structure, and response factors are thus intrinsically homogeneous, especially for first-generation fragments. As a proof-of-principle application in the sphingolipid field, isoenergetic fast scanning during LC separation of lipid extracts highlights the presence of unanticipated ceramides that can be quantified as equivalents of known analogs without resorting to the construction of individual calibration curves. The use of a scan mode coupled to the LC separation allows improving the amount of information on the sphingolipidome that can be extracted from complex samples, and discovering components with unusual or modified fatty acids. Among displayed proof-of principle examples are the sphingolipid fractions of organs and tissues of experimental animals, and of edible seeds and nuts
High-performance liquid chromatographic method to quantify total cysteine excretion in urine
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