RESUMEN
The Citrobacter freundii 62 cells immobilized in PAAG and possessing the tyrosine-phenol-lyase (TPL) activity catalyse the synthesis of 3,4-dihydroxyphenyl-L-alanine (DOPA) from pyrocatechol and ammonium pyruvate. The synthesis of DOPA was studied using both free and immobilized bacterial cells. When the concentration of pyrocatechol is over 0.1 M the TPL activity of the cells is inhibited. The concentration of pyrocatechol can be increased up to 0.3 M by using an equimolar mixture of pyrocatechol and boric acid. The addition of ascorbic acid as an antioxidant results in a lower TPL activity of both free and immobilized bacterial cells.
Asunto(s)
Citrobacter/enzimología , Dihidroxifenilalanina/biosíntesis , Resinas Acrílicas/farmacología , Catecoles/metabolismo , Cromatografía en Capa Delgada , Citrobacter/efectos de los fármacos , Dihidroxifenilalanina/análisis , Geles , Cinética , Piruvatos/metabolismo , Ácido Pirúvico , Tirosina Fenol-Liasa/metabolismoRESUMEN
The fumarate hydratase activity of intact cells was determined for 36 strains of Escherichia coli, receiver from the All-Union Collection of Microorganisms, to reveal a producer of L-malic acid. A research was made to find optimal media for cultivating microorganisms possessing the fumarate hydratase activity. Spectrophotometric and chromatographic methods were chosen to detect malic acid in the complete reaction mixture, which are available for kinetic study of the malic acid synthesis from potassium fumarate.
Asunto(s)
Escherichia coli/enzimología , Fumarato Hidratasa/metabolismo , Cromatografía en Gel/métodos , Cromatografía Líquida de Alta Presión/métodos , Medios de Cultivo/metabolismo , Escherichia coli/análisis , Fumarato Hidratasa/análisis , Cinética , Malatos/análisis , Malatos/biosíntesis , Espectrofotometría Ultravioleta/métodosRESUMEN
The kinetics of the fumarate hydratase (fumarase) reaction catalyzed by the cells of E. coli strain 85 at high concentrations of the substrate (potassium fumarate) were studied. An automatic procedure for determination of the reaction product--malonic acid--including the use of commercial malate dehydrogenase from porcine heart was developed. The fumarate activity of bacterial cells was studied at different concentrations of the substrate and at different pH values with intact and disrupted cells of E. coli 85 used as the enzyme source. The rate of the fumarase reaction in the E. coli cells was shown to depend on the diffusion and transport processes of the reagent transfer across the cell wall and the cytoplasmic membrane of bacterial cells. The pH optimum of the reaction in free E. coli cells (8-9) and the rate of malonic acid synthesis from potassium fumarate under optimal conditions, which varies within the concentration range of (6--13) x 10(-5) mkmole per mg of protein depending on the quality of cell, were determined.
Asunto(s)
Escherichia coli/enzimología , Fumarato Hidratasa/metabolismo , Concentración de Iones de Hidrógeno , Cinética , Malato Deshidrogenasa , Malonatos/análisisRESUMEN
E. coli 85 cells with a high aspartate-ammonia-lyase activity were immobilized through polyacrylamide gel incorporation. Proper conditions to assay aspartase activity of E. coli cells were developed. Kinetic patterns of aspartate-ammonia-lyase reaction catalyzed by free and immobilized E. coli 85 cells were studied. The synthesis of L-aspartic acid from ammonium fumarate had the following characteristics: specific activity of (4--6) . 10(-5) mmole/mg.sec for free cells and (6--8) . 10(-5) mmole/mg.sec for immobilized cells with their content in polyacrylamide gel of 5--10 mg protein per g wet gelm pH 8.3--10.0.
Asunto(s)
Ácido Aspártico/biosíntesis , Escherichia coli/metabolismo , Fumaratos/metabolismo , Compuestos de Amonio Cuaternario/metabolismo , Concentración de Iones de Hidrógeno , Cinética , EstereoisomerismoRESUMEN
The effects of temperature (45--55 degrees) and duration of thermal treatment on the L-aspartase activity of free and immobilized on polyacrylamide gel cells of E. coli, strain 85 were studied. It was found that preliminary thermal treatment of the cells at 50 degrees for 40--60 min is optimal for a high aspartase activity. Within the temperature interval of 20--55 degrees the temperature dependence of effective rate constants of L-aspartate synthesis obeys the Arrhenius equation, whereas the effective energy of activation is decreased from 12,6 to 3,6 kcal/mole, when the "activation" of the cells shows an increase.
Asunto(s)
Amoníaco-Liasas/metabolismo , Aspartato Amoníaco-Liasa/metabolismo , Escherichia coli/enzimología , Cinética , TemperaturaRESUMEN
The resistances to heat and trypsin hydrolysis served as indirect indices of conformational flexibility of glutamate dehydrogenase molecules. No difference in heat resistance was found between crystalline eletrophoretically homogeneous preparations of glutamate dehydrogenase from liver mitochondria of two species of frogs, the more southern Rana ridibunda and the more northern R. temporaria. However, glutamate dehydrogenase from R. ridibunda is digested by trypsin at a lower rate than that from R. temporaria, which may be explained by its lower conformational flexibility. Therefore positive correlation between conformational flexibility of glutamate dehydrogenase and mean ambient temperature of the species studied is revealed only with respect to resistance to proteolysis.