Characterisation of nitrate reductase in the marine macroalga Kappaphycus alvarezii (Rhodophyta)

• Published in: Aquatic botany Vol. 78; no. 4; pp. 295 - 305
• Main Authors: Granbom, Malena, Chow, Fungyi, Lopes, Patrı́cia F, de Oliveira, Mariana C, Colepicolo, Pio, de Paula, Edison José, Pedersén, Marianne
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-04-2004
• Subjects: Circadian rhythm; Diurnal rhythm; Kappaphycus alvarezii; Marine; Nitrate reductase; ISEW, Philippines; Kappaphycus alvarezii; Diurnal rhythm; Circadian rhythm; Nitrate reductase
• ISSN: 0304-3770; 1879-1522
• DOI: 10.1016/j.aquabot.2003.11.001

Nitrate reductase (NR) of the marine red macroalga
Kappaphycus alvarezii (Doty) Doty ex P. Silva was examined regarding the biochemical characteristics and daily fluctuations in activity. NR activity was maximum at pH 8.0 and stable over a wide range of temperatures, with an optimum at 23
°C. The highest specific activity measured in a crude extract was 0.16
U
mg
−1 protein. Apical parts of the algal thallus showed 1.5 times higher activity compared to basal parts. The NR was NADH-specific (EC 1.6.6.1), since no activity was found when NADPH was used as an electron donor. The apparent Michaelis–Menten (
K
M) constants for nitrate and NADH were 30 and 5
μM, respectively. The stability of NR was assessed by storing the crude extract in different temperatures. Stored at 4
°C, the crude extract maintained high NR activity for 1 week.
NR activity exhibited a daily rhythm in algae grown under either a light–dark cycle of 55
μmol
photons
m
−2
s
−1 or in constant light of 100
μmol
photons
m
−2
s
−1, with maximal activity during the midday phase. The results thus indicate that the expression of NR activity may be under circadian control.