, Volume 133, Issue 2, pp 191-196

Carboxylating enzymes and pathway of photosynthetic carbon assmilation in different marine algae—Evidence for the C4-pathway?

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Abstract

Experiments on short-term photosynthesis in H14CO3 - (2–5 s) using various species of different algal classes resulted in predominant 14C-labelling (>90% of total 14C-incorporation) of phosphorylated compounds. The percentage of malate and aspartate usually accounts for distinctly less than 10% of the total 14C-labelling. These findings are consistent with data from enzymatic analyses, since 97–100% of the carboxylation capacity is due to ribulose-1.5-biphosphate carboxylase (EC 4.1.1.39) in Rhodophyceae and Chlorophyceae. Phaeophyceae are generally characterized by considerable activity of phosphoenolpyruvate carboxykinase (EC 4.1.1.32): at least 10% of carboxylation is confined to this enzyme. Similar ratios are obtained when rates of photosynthesis and of light-independent CO2-fixation are compared. Activity of phosphoenolpyruvate carboxylase (EC 4.1.1.31) could not be detected in the species investigated. The results are discussed with emphasis on the pathway of photosynthetic carbon assimilation in marine algae.

Dedicated to Professor H. Fischer, Bonn, on his 65th birthday