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Photosynthetic carbon assimilation in the blue‐green alga Coccochloris peniocystis
Author(s) -
COLEMAN J. R.,
COLMAN B.
Publication year - 1981
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/1365-3040.ep11604546
Subject(s) - photosynthesis , phosphoenolpyruvate carboxykinase , bicarbonate , phosphoenolpyruvate carboxylase , carbon fixation , assimilation (phonology) , decarboxylation , chemistry , biochemistry , kinetics , rubisco , enzyme , pyruvate carboxylase , metabolism , botany , biophysics , biology , catalysis , organic chemistry , linguistics , philosophy , physics , quantum mechanics
. Cells of the blue‐green alga Coccochloris peniocystis , grown at air levels of CO 2 , were exposed to [ l4 C]bicarbonate in the light for periods of 0.5 to 2.0 s followed by exposure to unlabelled bicarbonate for longer periods of time in the light. The kinetics of tracer movement during these pulse‐chase experiments demonstrate that the principal mechanism of CO 2 fixation in this alga is the C 3 ‐pathway although an appreciable amount of the C 4 acid aspartate is found as one of the initial products of photosynthesis. Degradation of the labelled aspartate revealed that after 20 s of illumination, over 95% of the radioactivity was located in the β‐carboxyl of this C 4 acid. This alga possesses little, if any, capacity for either the enzymatic decarboxylation of C 4 acids or the regeneration of phosphoenolpyruvate (PEP) from pyruvate mediated by the enzyme pyruvate, P i dikinase. These data further demonstrate the lack of a functional C 4 ‐pathway in this alga.