Premium
OXYGEN CONSUMPTION ASSOCIATED WITH FERRIC REDUCTASE ACTIVITY AND IRON UPTAKE BY IRON‐LIMITED CELLS OF CHLORELLA KESSLERI (CHLOROPHYCEAE)
Author(s) -
Middlemiss Jocelyn K.,
Anderson Andrea M.,
Stratilo Chad W.,
Weger Harold G.
Publication year - 2001
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1046/j.1529-8817.2001.037003393.x
Subject(s) - ferric , reductase , ferrous , superoxide dismutase , catalase , biology , chlorella , oxygen , chlorophyceae , superoxide , photosynthesis , biochemistry , chemistry , algae , inorganic chemistry , botany , chlorophyta , enzyme , organic chemistry
Plasma membrane ferric reductase activity was enhanced 5‐fold under iron limitation in the unicellular green alga Chlorella kessleri Fott et Nováková. Furthermore, ferric reductase activity in iron‐limited cells was approximately 50% higher in the light than in the dark. In contrast, iron uptake rates of iron‐limited cells were unaffected by light versus dark treatments. Rates of iron uptake were much lower than rates of ferric reduction, averaging approximately 2% of the dark ferric reduction rate. Ferric reduction was associated with an increased rate of O 2 consumption in both light and dark, the increase in the light being approximately 1.5 times as large as in the dark. The increased rate of O 2 consumption could be decreased by half by the addition of catalase, indicating that H 2 O 2 is the product of the O 2 consumption and that the increased O 2 consumption is nonrespiratory. The stimulation of O 2 consumption was almost completely abolished by the addition of bathophenanthroline disulfonate, a strong chelator of Fe 2 + . Anaerobic conditions or the presence of exogenous superoxide dismutase affected neither ferric reduction nor iron uptake. We suggest that the O 2 consumption associated with ferric reductase activity resulted from superoxide formation from the aerobic oxidation of Fe 2 + , which is the product of ferric reductase activity. At saturating concentrations of Fe 3 + chelates, ferric reductase activity is much greater than the iron uptake rate, leading to rapid oxidation of Fe 2 + and superoxide generation. Therefore, O 2 consumption is not an integral part of the iron assimilation process.