Phosphoenolypyruvate Carboxykinase from the Marine Diatom Skeletonema costatum and the Phaeophyte Laminaria setchellii. II. Immunological Characterization and Subcellular Localization

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Abstract
Phosphoenolpyruvate carboxykinase (PEPCK) is responsible for light-independent carbon fixation (LICF) processes in a wide range of marine algae, however, little is known about the intracellular localization of the enzyme among different algal groups. Antibodies against PEPCK recognized polypeptides in electrophoresed samples of cell-free extracts from only non-green phytoplankton and macrophytic Phaeophyta while antibodies against phosphoenolpyruvate carboxylase (PEPC) recognized polypeptides in samples of only chlorophytes. This supports the hypothesis that PEPCK is the dominant enzyme in LICF processes in chromophytes while PEPC is the enzyme responsible for non-photosynthetic processes in the chlorophytes. The enzyme PEPCK was immuno-localized in the chloroplasts of the diatom Skeletonema costatum and the kelp Laminaria setchellii which differs from the localization of the enzymes in most vascular plants. While LICF processes occur in the cytoplasm of most vascular plants, the results of this study suggest that in marine chromophytes, LICF processes are catalyzed in the chloroplasts and that the flow of carbon varies between these groups of autotrophs.