RESUMEN
Vitamins are a vast group of fundamental organic compounds, which are not produced by the human body but are essential for the living organisms' good health. Vitamins B6 and B12 belong to the same group of hydrophilic vitamins. Structurally unrelated, they share the same purpose as essential components for normal cellular operation, growth and development. Vitamin B6 is an enzymatic co-factor that is vital for countless biochemical reactions, and is also important in sugar and fatty acid metabolization. It encompasses three natural and inter-convertible pyridine-derivatives: pyridoxine, pyridoxal and pyridoxamine. Vitamin B12 is a cobalt organometallic complex also indispensable in numerous human physiological functions. It has four bioactive forms: cyanocobalamin, methylcobalamin, hydroxocobalamin and 5'-deoxyadenosylcobalamin, and only a few prokaryotes have the ability to biosynthesize cobalamin. This work reviews the significant aspects of vitamins B6 and B12: their vital roles, consequences of deficit; food sources; and methods of determination and respective matrices, with heavy emphasis on chromatographic techniques developed within the last two decades.
Asunto(s)
Piridoxina , Vitamina B 6 , Humanos , Piridoxina/análisis , Prevalencia , Piridoxal , Vitaminas , Vitamina B 12RESUMEN
The pH gating of human AQP3 and its effects on both water and glycerol permeabilities have been fully characterized for the first time using a human red blood cell model (hRBC). For comparison, the effects of pH on the gating of rat AQP3 have also been characterized in yeast. The obtained results highlight similarities as well as differences between the two isoforms. In addition, we investigated the molecular mechanism of hAQP3 pH gating in silico, which may disclose new pathways to AQP regulation by small molecule inhibitors, and therefore may be important for drug development.
Asunto(s)
Acuaporina 3/química , Acuaporina 3/metabolismo , Diseño de Fármacos , Activación del Canal Iónico/efectos de los fármacos , Animales , Acuaporina 3/antagonistas & inhibidores , Acuaporina 3/genética , Línea Celular , Permeabilidad de la Membrana Celular , Clonación Molecular , Simulación por Computador , Expresión Génica , Glicerol/química , Glicerol/metabolismo , Humanos , Enlace de Hidrógeno , Concentración de Iones de Hidrógeno , Cinética , Modelos Moleculares , Unión Proteica , Conformación Proteica , Transporte de Proteínas , RatasRESUMEN
Two genes encoding Na(+)-ATPases from Debaryomyces hansenii were cloned and sequenced. The genes, designated ENA1 from D. hansenii (DhENA1) and DhENA2, exhibited high homology with the corresponding genes from Schwanniomyces occidentalis. DhENA1 was expressed in the presence of high Na(+) concentrations, while the expression of DhENA2 also required high pH. A mutant of Saccharomyces cerevisiae lacking the Na(+) efflux systems and sensitive to Na(+), when transformed with DhENA1 or DhENA2, recovered Na(+) tolerance and also the ability to extrude Na(+).
Asunto(s)
Adenosina Trifosfatasas/metabolismo , Proteínas de Transporte de Catión , Clonación Molecular , Proteínas de Saccharomyces cerevisiae , Saccharomycetales/genética , Cloruro de Sodio/metabolismo , ATPasa Intercambiadora de Sodio-Potasio/metabolismo , Adenosina Trifosfatasas/genética , Concentración de Iones de Hidrógeno , Datos de Secuencia Molecular , Saccharomycetales/crecimiento & desarrollo , Saccharomycetales/metabolismo , ATPasa Intercambiadora de Sodio-Potasio/genéticaRESUMEN
The effect of Na+ and K+ on growth and thermal death of Debaryomyces hansenii and Saccharomyces cerevisiae were compared under stress conditions as those commonly found in food environments. At the supraoptimal temperature of 34 degrees C both cations at concentrations of 0.5 M stimulated growth of D. hansenii, while K+ had no effect and Na+ inhibited growth of S. cerevisiae. At 8 degrees C, close to the minimum temperature for growth in both species, both cations inhibited both yeasts, this effect being more pronounced with Na+ in S. cerevisiae. At extreme pH values (7.8 and 3.5) both cations at concentrations of 0.25 M stimulated D. hansenii while Na+ inhibited S. cerevisiae. K+ inhibited this yeast at pH 3.5. Thermal inactivation rates, measured at 38 degrees C in D. hansenii and at 48 degrees C in S. cerevisiae, decreased in the presence of both cations. This protective effect could be observed in a wider range of concentrations in D. hansenii. These results call the attention to the fact that not all yeasts have the same behaviour on what concerns synergy or antagonism of salt together with other stress factors and should be taken into consideration in the establishment of food preservation procedures.
Asunto(s)
Potasio/farmacología , Saccharomycetales/efectos de los fármacos , Sodio/farmacología , Saccharomyces cerevisiae/efectos de los fármacos , Saccharomyces cerevisiae/crecimiento & desarrollo , Saccharomycetales/crecimiento & desarrollo , Sorbitol/farmacología , TemperaturaRESUMEN
The effects of KCl, NaCl, and LiCl on the growth of Debaryomyces hansenii, usually considered a halotolerant yeast, and Saccharomyces cerevisiae were compared. KCl and NaCl had similar effects on D. hansenii, indicating that NaCl created only osmotic stress, while LiCl had a specific inhibitory effect, although relatively weaker than in S. cerevisiae. In media with low K+, Na+ was able to substitute for K+, restoring the specific growth rate and the final biomass of the culture. The intracellular concentration of Na+ reached values up to 800 mM, suggesting that metabolism is not affected by rather high concentrations of salt. The ability of D. hansenii to extrude Na+ and Li+ was similar to that described for S. cerevisiae, suggesting that this mechanism is not responsible for the increased halotolerance. Also, the kinetic parameters of Rb+ uptake in D. hansenii (Vmax, 4.2 nmol mg [dry weight]-1 min-1; K(m), 7.4 mM) indicate that the transport system was not more efficient than in S. cerevisiae. Sodium (50 mM) activated the transport of Rb+ by increasing the affinity for the substrate in D. hansenii, while the effect was opposite in S. cerevisiae. Lithium inhibited Rb+ uptake in D. hansenii. We propose that the metabolism of D. hansenii is less sensitive to intracellular Na+ than is that of S. cerevisiae, that Na+ substitutes for K+ when K+ is scarce, and that the transport of K+ is favored by the presence of Na+. In low K+ environments, D. hansenii behaved as a halophilic yeast.