Asunto(s)
Alcaligenes/enzimología , Flavinas/biosíntesis , Fosfotransferasas (Aceptor de Grupo Alcohol) , Vitamina B 12/biosíntesis , Alcaligenes/efectos de los fármacos , Alcaligenes/genética , Bencimidazoles/biosíntesis , Bencimidazoles/farmacología , Betaína/farmacología , Cobalto/metabolismo , Medios de Cultivo , Fermentación/efectos de los fármacos , Flavinas/genética , Flavinas/farmacología , Fosfotransferasas/metabolismo , Vitamina B 12/genética , Vitamina B 12/farmacologíaRESUMEN
The pathway of vitamin B-12 biosynthesis in anaerobic bacteria differs in several respects from the pathway found in aerobic or aerotolerant microorganisms. The aim of this investigation was to elucidate the formation of the 5,6-dimethylbenzimidazole part and the amide groups of vitamin B-12 in anaerobic bacteria. [15N]Ammonium chloride or L-[amido-15N]glutamine or a mixture of [15N]ammonium sulfate and [15N]glycine was added to fermentations with Eubacterium limosum. The vitamin B-12 isolated from these fermentations was methylated and degraded to cobinamide and 1,5,6-trimethylbenzimidazole. The amide groups of cobinamide were hydrolyzed and the amide nitrogen of the side chains a, b, c, d, e and g trapped as benzamide. The 15N incorporation was determined by mass spectroscopy. Thus in the experiment with [15N]ammonium chloride the benzamide and the 1,5,6-trimethylbenzimidazole contained 9.6% 15N, whereas in the experiment with L-[amido-15N]glutamine 37.5% of the molecules were 15N labeled. The 1H-NMR spectrum of 1,5,6-trimethylbenzimidazole revealed that the 15N from the ammonium salts and from glutamine was incorporated into N-3 of the 5,6-dimethylbenzimidazole moiety of vitamin B-12. With a mixture of [15N]ammonium sulfate and [15N]glycine both nitrogens of 5,6-dimethylbenzimidazole became 15N-labeled. These experiments demonstrate that in E. limosum the amide nitrogen of glutamine is not only the precursor of the six amide groups of the corrin ring, but also of N-3 of the 5,6-dimethylbenzimidazole moiety of vitamin B-12.
Asunto(s)
Amidas/biosíntesis , Bencimidazoles/biosíntesis , Eubacterium/metabolismo , Vitamina B 12/biosíntesis , Anaerobiosis , Corrinoides , Fermentación , Hidrólisis , Espectroscopía de Resonancia Magnética , MetilaciónRESUMEN
Pharmacokinetics of [14C]omeprazole and its metabolites were studied after single intravenous and oral doses of 20 and 40 mg, respectively, to 12 patients with chronic renal insufficiency. Blood samples for determination of total radioactivity, omeprazole, OH-omeprazole, sulfone, and sulfide were taken for 24 hours. Urine was collected over 96 hours for determination of total radioactivity and during the first 24 hours for additional assay of omeprazole and metabolites. The mean systemic availability was 70%. The mean plasma t1/2 of omeprazole was 0.6 hours. Unchanged omeprazole was not measurable in urine. Derived pharmacokinetic constants of intact omeprazole were within the range of those reported in healthy individuals. The accumulated 24-hour excretion of radioactive metabolites was related significantly to creatinine clearance. The cumulative excretion of total radioactivity in urine over 96 hours in percent of given dose varied between 25% and 83%.
Asunto(s)
Bencimidazoles/biosíntesis , Bencimidazoles/sangre , Fallo Renal Crónico/sangre , 2-Piridinilmetilsulfinilbencimidazoles , Adulto , Anciano , Proteínas Sanguíneas/metabolismo , Femenino , Humanos , Cinética , Masculino , Matemática , Persona de Mediana Edad , OmeprazolRESUMEN
1. Homogenates of Propionibacterium freudenreichii transform riboflavin into 5,6-dimethylbenzimidazole. This process is stimulated by nicotinamide. Homogenates of Propionibacterium shermanii form only small amounts of 5,6-dimethylbenzimidazole from riboflavin in the absence of nicotinamide, but also form appreciable amounts in the presence of nicotinamide. 2. The stimulation of the 5,6-dimethylbenzimidazole-forming system by nicotinamide shows a lag phase which is abolished by preincubation of the homogenate with nicotinamide. Since no lag phase is observed when nicotinamide is replaced by nicotinate, nicotinate seems to be the true stimulating agent. These observations are in agreement with the fact that nicotinamide is rapidly split to nicotinate in homogenates of P. freudenreichii. 3. The 5,6-dimethylbenzimidazole-forming homogenate system is only active at a high buffer concentration (0.3--0.5 M) and in the presence of oxygen. The system has a pronounced oxygen optimum. 4. Flavin mononucleotide and flavin-adenine dinucleotide are better substrates for the 5,6-dimethylbenzimidazole-forming homogenate system than riboflavin. But with [1'-14C]riboflavin as substrate the specific radioactivity of 5,6-dimethylbenzimidazole is higher than the specific radioactivity of flavin--adenine dinucleotide and lower than the specific radioactivie substrate for the formation of 5,6-dimethylbenzimidazole. 5. A tentative reaction sequence for the transformation of flavin mononucleotide into 5,6-dimethylbenzimidazole is discussed.
Asunto(s)
Bencimidazoles/biosíntesis , Propionibacterium/metabolismo , Vitamina B 12/biosíntesis , Mononucleótido de Flavina/metabolismo , Flavina-Adenina Dinucleótido/metabolismo , Niacinamida/farmacología , Ácidos Nicotínicos/metabolismo , Riboflavina/metabolismoRESUMEN
The content of flavins and vitamin B12 was studied in the cultures of Propionibacterium shermanii. The limited ability of propionic bacteria to synthesize 5,6-dimethylbenzimidazole, the nucleotide base in the true forms of vitamin B12, was found to be caused by a deficiency of the biogenetic precursor (riboflavin). Exogenous 5,6-dimethylbenzimidazole had no effect on the processes of flavinogenesis. In the absence of the nucleotide base, the yield of the true forms of vitamin B12 increased upon aeration of cultures which were grown for four days on an iron-deficient medium in the anaerobic conditions.
Asunto(s)
Flavinas/metabolismo , Propionibacterium/metabolismo , Vitamina B 12/biosíntesis , Bencimidazoles/biosíntesis , Cobalto/farmacología , Medios de Cultivo , Mononucleótido de Flavina/metabolismo , Flavina-Adenina Dinucleótido/metabolismo , Hierro/farmacología , Propionibacterium/efectos de los fármacos , Riboflavina/metabolismo , Factores de TiempoRESUMEN
1. In Clostridium thermoaceticum 5-hydroxybenzimidazole is methylated to 5-methoxybenz-imidaxole and transformed to 5-methoxybenzimidazolylcobamide. 5-Hydroxybenzimidazolycobamide is also methylated to 5-methoxybenzimidazolylcobamide. These results indicate a possible precursor function of 5-hydroxybenzimidazole in the biosynthesis of 5-methoxybenzimidazole. 2. The same microorganism uses benzimidazole to form benzimidazolylcobamide. This or externally added benzimidazolylcobamide, although taken up by the cells, is not further transformed (i.e. hydroxylated and methylated to 5-methoxybenzimdazolylcobamidel). This excludes a precursor function of benzimidazole in the biosynthesis of 5-methoxybenzimidazole. 3. Contrary to the biosynthesis of 5,6-dimethylbenzimidazole, 5-methoxybenzimidazole is not formed from riboflavin, but riboflavin inhibits the growth and the production of 5-methoxybenzimidazolylcobamide in Clostridium thermoaceticum. A tentative scheme for the biosynthesis of 5-methoxybenzimidazole via a riboflavin analog is discussed.