Author:
Nakamura Yoshiko,Kanakagiri Saradadevi,Van Kyujung,He Wei,Spalding Martin H
Abstract
One of the most notable contrasts between the photorespiratory pathway of higher plants and that of many of the green algae including Chlamydomonas reinhardtii lies in the enzymes that serve for oxidation of glycolate to glyoxylate. The gene disrupted by insertional mutagenesis in a high-CO2-requiring mutant, HCR89, of C. reinhardtii was determined to encode glycolate dehydrogenase (EC 1.1.99.14), which serves as the counterpart of glycolate oxidase (EC 1.1.3.15) in classical higher plant photorespiration. Neither glycolate nor D-lactate oxidation from the membrane fraction of HCR89 was detected. Excretion of over-accumulated glycolate into media due to the absence of glycolate dehydrogenase activity was observed for HCR89 under both high- and low-CO2conditions. Chlamydomonas glycolate dehydrogenase, CrGDH, with a molecular mass of 118 851 Da, comprises a relatively hydrophobic N-terminal region, a FAD-containing domain homologous to the D subunit of the glycolate oxidase complex from Escherischia coli, and an ironsulfur cluster containing domain homologous to the C subunit of anaerobic glycerol-3-phosphate dehydrogenase complex from Escherichia coli. The second Cys residue in the second ironsulfur cluster motif of CrGDH is replaced by Asp, as CxxDxxCxxxCP, indicating the second ironsulfur cluster coordinates most likely 3Fe4S instead of 4Fe4S. The membrane association of the glycolate dehydrogenase activity agrees with three predicted transmembrane regions on the ironsulfur domain.Key words: algae, Chlamydomonas, CO2, glycolate, lactate, mitochondria, photorespiration, photosynthesis.
Publisher
Canadian Science Publishing
Cited by
57 articles.
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