L-Histidine

in ;English;, ;Spanish;La carnosina, dipéptido formado por los aminoácidos ß-alanina y L-histidina, tiene importantes funciones fisiológicas entre las que destaca su función antioxidante y las relacionadas con la memoria y el aprendizaje. Sin embargo, en relación con el ejercicio, las funciones más importantes serían las relacionadas con la contractilidad muscular, al mejorar la sensibilidad al calcio en las fibras musculares, y la función reguladora del pH. De este modo, se ha propuesto que la carnosina es el principal tampón intracelular, pudiendo llegar a contribuir hasta un 7-10% en la capacidad buffer o tampón. Dado que la síntesis de carnosina parece estar limitada por la disponibilidad de ß-alanina, la suplementación con este compuesto ha ido ganando cada vez más popularidad entre la población deportista. Por ello, el objetivo del presente estudio de revisión bibliográfica ha sido el de estudiar todos aquellos trabajos de investigación que han comprobado el efecto de la suplementación con ß-alanina sobre el rendimiento deportivo. Por otra parte, también, se ha intentado establecer una posología específica que, maximizando los posibles efectos beneficiosos, reduzca al mínimo la parestesia, el principal efecto secundario presentado como respuesta a la suplementación.

Peroxide-induced oxidative modifications of haem proteins such as myoglobin and haemoglobin can lead to the formation of a covalent bond between the haem and globin. These haem to protein cross-linked forms of myoglobin and haemoglobin are cytotoxic and have been identified in pathological conditions in vivo. An understanding of the mechanism of haem to protein cross-link formation could provide important information on the mechanisms of the oxidative processes that lead to pathological complications associated with the formation of these altered myoglobins and haemoglobins. We have re-examined the mechanism of the formation of haem to protein cross-link to test the previously reported hypothesis that the haem forms a covalent bond to the protein via the tyrosine 103 residue (Catalano, C. E., Choe, Y. S., Ortiz de Montellano, P. R., J. Biol. Chem. 1989, 10534 - 10541). Comparison of native horse myoglobin, recombinant sperm whale myoglobin and Tyr(103) --> Phe sperm whale mutant shows that, contrary to the previously proposed mechanism of haem to protein cross-link formation, the absence of tyrosine 103 has no impact on the formation of haem to protein cross-links. In contrast, we have found that engineered myoglobins that lack the distal histidine residue either cannot generate haem to protein cross-links or show greatly suppressed levels of modified protein.

Heme nitric oxide/oxygen sensing (H-NOX) domains are direct NO sensors that regulate a variety of biological functions in both bacteria and eukaryotes. Previous work on H-NOX proteins has shown that upon NO binding, a conformational change occurs along two glycine residues on adjacent helices (termed the glycine hinge). Despite the apparent importance of the glycine hinge, it is not fully conserved in all H-NOX domains. Several H-NOX sensors from the family Flavobacteriaceae contain a native alanine substitution in one of the hinge residues. In this work, the effect of the increased steric bulk within the Ala-Gly hinge on H-NOX function was investigated. The hinge in Kordia algicida OT-1 ( Ka H-NOX) is composed of A71 and G145. Ligand-binding properties and signaling function for this H-NOX were characterized. The variant A71G was designed to convert the hinge region of Ka H-NOX to the typical Gly-Gly motif. In activity assays with its cognate histidine kinase (HnoK), the wild type displayed increased signal specificity compared to A71G. Increasing titrations of unliganded A71G gradually inhibits HnoK autophosphorylation, while increasing titrations of unliganded wild type H-NOX does not inhibit HnoK.