title: Photosynthetic CO2 fixation and ribulose bisphosphate carboxylase/oxygenase activity of Nostoc sp. strain UCD 7801 in symbiotic association with Anthoceros punctatus.
abstract: The cyanobacterium Nostoc sp. strain UCD 7801, immediately after separation from pure cultures of a reconstituted symbiotic association with the bryophyte Anthoceros punctatus, exhibited a rate of light-dependent CO2 fixation that was eightfold lower than that measured in the free-living growth state. Ribulose bisphosphate carboxylase/oxygenase (RuBPC/O) specific activity was also eightfold lower in cell extracts of symbiotic strain 7801 relative to that in free-living cultures. The in vitro activity from symbiotic strain 7801 could not be increased by incubation under the standard RuBPC/O activation conditions. Polyclonal antibodies against the RuBPC/O large subunit were used in an enzyme-linked immunosorbent assay to determine that RuBPC/O accounted for 4.3 and 5.2% of the total protein in cell extracts of strain 7801 grown in symbiotic and free-living states, respectively. The results imply that the regulation of RuBPC/O activity in the symbiotic growth state is by a posttranslational mechanism rather than by an alteration in RuBPC/O protein synthesis. The amount of carboxyarabinitol bisphosphate required to irreversibly inhibit RuBPC/O activity of sybiotic cell extracts was 80% of that required for extracts of free-living cultures. This result indicates that any covalent modification of RuBPC/O in symbiotically associated Nostoc cells did not interfere with the ribulose bisphosphate binding site, since inactive enzyme also bound carboxyarabinitol bisphosphate.
authors.affiliation: Department of Microbiology, University of California, Davis 95616.
authors.forename: N A
authors.initials: NA
authors.lastname: Steinberg
authors.forename: J C
authors.initials: JC
authors.lastname: Meeks
mesh_terms: D015153:Blotting, Western; D002245:Carbon Dioxide / Q000378:metabolism; D000458:Cyanobacteria / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D004237:Diuron / Q000494:pharmacology; D004351:Drug Resistance; D004797:Enzyme-Linked Immunosorbent Assay; D007700:Kinetics; D008027:Light; D046911:Macromolecular Substances; D008970:Molecular Weight; D010788:Photosynthesis; D018521:Plant Physiological Phenomena; D012273:Ribulose-Bisphosphate Carboxylase / Q000302:isolation & purification / Q000378:metabolism*; D013559:Symbiosis
chemical_list: D046911:Macromolecular Substances; D002245:Carbon Dioxide; D004237:Diuron; D012273:Ribulose-Bisphosphate Carboxylase