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Provedor de dados:  Rev. Bras. Bot.
País:  Brazil
Título:  Characterization of nitrate reductase activity in vitro in Gracilaria caudata J. Agardh (Rhodophyta, Gracilariales)
Autores:  Chow,Fungyi
Capociama,Fernanda V.
Oliveira,Mariana C. de
Data:  2007-03-01
Ano:  2007
Palavras-chave:  Agarophyte
Gracilaria caudata
Nitrate reductase
Nitrogen metabolism
Resumo:  The marine red alga Gracilaria caudata J. Agardh has been used in Brazil for agar extraction, mainly in the northeast region of the country. Nitrogen availability is the most important abiotic factor in seawater that limits the growth of seaweeds. The enzyme nitrate reductase (NR) is the key regulatory point in the nitrogen assimilation in photosynthetic organisms. This study describes an in vitro assay, characterizing the enzymatic activity of NR in terms of kinetic constants and stability, its oscillation during the day and glucose effect on NR modulation. Maximal peaks of NR activity were recorded at 20 ºC and pH 8.0. The enzymatic stability in crude extracts stored at 3 ± 1 ºC decreased significantly after 48 hours. Apparent Michaelis-Menten constants (K M) for NADH and nitrate were 22 µM and 3.95 mM, respectively. Gracilaria caudata NR activity showed an oscillation under light:dark photoperiod (14:10 hours LD) with 3-fold higher activity during the light phase, peaking after 10 hours of light. Under optimal assay conditions, the maximal activity was 92.9 10-3 U g-1. The addition of glucose induced the enzymatic activity during the light and dark phase, evidencing a possible modulation of this enzyme by the photosynthesis. This relationship can be explained by the need of carbon skeletons, produced by the photosynthetic process, to incorporate the intermediary metabolites of nitrate assimilatory pathway, avoiding the toxic intracellular accumulation of nitrite and ammonium. The optimization of enzymatic assay protocols for NR is essential to establish appropriate conditions to study nutritional behaviour, compare different taxonomic groups and to understand its regulatory mechanism.
Tipo:  Info:eu-repo/semantics/article
Idioma:  Inglês
Editor:  Sociedade Botânica de São Paulo
Relação:  10.1590/S0100-84042007000100012
Formato:  text/html
Fonte:  Brazilian Journal of Botany v.30 n.1 2007
Direitos:  info:eu-repo/semantics/openAccess

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