109 research outputs found
β Oxidative cleavage of octanoyl and dodecanoyl CoA in rat liver cytoplasm
No full text[12 14C] Dodecanoyl CoA and [8 14C] octanoyl CoA were tested as substrates for shortening the chain by two carbon atoms using both the 105,000 x g soluble fraction and the sonicated mitochondrial fraction of rat liver homogenate as the enzyme source. Both substrates were metabolized by the cytoplasmic enzymes giving rise to the accumulation of intermediates of the β oxidation process without formation of two carbon units from the methyl carbon of the acyl residue. A new method is described which allows quantitative estimation of volatile fatty acids formed by β oxidation of dodecanoyl and octanoyl Coenzyme A
A simple model for studies on the regulation of cholesterol synthesis using freshly isolated hepatocytes
No full textRat hepatocytes isolated by the procedure described here showed 3-hydroxy-3-methylglutaryl-CoA reductase activity in the range of that reported for rat liver at the maximum of the circadian cycle, even if they were taken from rats at the time of the minimum. The enzyme was present in cells as both its active dephosphorylated (20 +/- 8%) and the inactive phosphorylated forms. The enzyme activity and the ratio between the two forms were unaltered during 3 h of cell incubation. 25-Hydroxycholesterol (50 microM) induced about 50% inhibition of 3-hydroxy-3-methylglutaryl-CoA reductase activity during 1 h incubation but the relative amount of the two forms was not modified by the sterol. Cells isolated by the described procedure may therefore be a useful tool in studies on the regulation of cholesterol neogenesis, both through the synthesis of the enzyme, which can be shown by measuring the activity after complete dephosphorylation of the enzyme, and via the rapid reversible shift of the inactive to the active form, resulting from the ratio between the two enzyme forms. The latter mechanism for the modulation of cholesterol synthesis cannot be tested in cell cultures because full activation of the enzyme occurs during hepatocyte plating
Lack of conversion of xanthine dehydrogenase to xanthine oxidase during warm renal ischemia
No full textAbstractIrreversible transformation of xanthine dehydrogenase (XDH) to xanthine oxidase (XO) during ischemia was determined measuring XDH and total enzyme activity in kidneys before and after 60 min of clamp of the renal pedicle. Tissue levels of adenine nucleotides, xanthine and hypoxanthine were used as indicators of ischemia. After 60 min of clamping, ATP levels decreased by 72% with respect to controls whereas xanthine and hypoxanthine progressively reached tissue concentrations of 732 ± 49 and 979 ± 15 nmol· g tissue −1, respectively. Both total and XDH activities in ischémie kidneys (30 ± 15 and 19 ± 1 nmol·min−1 -g tissue−1) were significantly lower than in controls when expressed on a tissue weight basis. The fraction of enzyme in the XDH form was however unchanged indicating that the reduction of the nucleotide pool is not accompanied by induction of the type-O activity of xanthine oxidase
Evaluation of 3-hydroxy-3- methylglutaryl-CoA reductase activity by multiplet-selected ion monitoring
No full textA new method for the evaluation of 3-hydroxy-3-methylglutaryl-CoA reductase activity is described, based on the multiple-selected ion monitoring of the amount of mevalonate formed in incubations of 3-hydroxy-3-methylglutaryl-CoA with microsomal proteins. Analysis is carried out on crude extracts using deuterated mevalonic acid lactone as internal standard. The sensitivity of the technique allows the quantitative evaluation of mevalonate in microassays (100 μg microsomal protein) of the enzyme activity at the minimum value of the diurnal rhythm
Simple and selective one-pot replacement of the N-methyl group of tertiary amines by quaternization and demethylation with sodium sulfide or potassium thioacetate: an application to the synthesis of pergolide
No full textThe paper describes a mild, selective, and rapid replacement of an N-methyl group of tertiary amines with other alkyl groups via a simple one-pot procedure. This transformation is easily achieved by preparation of the appropriate quaternary ammonium salt in sulfolane and in situ treatment with sodium sulfide or potassium thioacetate. The protocol is successfully applied to the transformation of dihydrolysergol, dextromethorphan and laudanosine (as models of ergot and opium N-methyl alkaloids) into various A-alkyl congeners
Erratum to ‘‘Validation of methyl malondialdehyde as internal standard for malondialdehyde detection by capillary electrophoresis’’ [Anal. Biochem. 307 (2002)92–98]
No full text
Cleavage of benzyloxycarbonyl-5-oxazolidinones to α-benzyloxycarbonylamino-α-alkyl esters by alcohols and sodium hydrogen carbonate
No full textThe reaction of benzyloxycarbonyl-5-oxazolidinones with alcohols and sodium hydrogen carbonate to afford the corresponding benzyloxycarbonyl esters is described
NO DOCUMENTABLE ROLE FOR XANTHINE-OXIDASE IN THE PATHOGENESIS OF HEPATIC IN-VIVO ISCHAEMIA/REPERFUSION INJURY
No full textAn 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
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