Phosphoenolpyruvate carboxykinase from the marine diatom Skeletonema costatum and the phaeophyte Laminaria setchellii. II. Immunological characterization and subcellular localization

Phosphoenolpyruvate carboxykinase (PEPCK) is responsible for light-independ ent carbon fixation (LICF) processes in a wide range of marine algae, howev er, little is known about the intracellular localization of the enzyme amon g different algal groups. Antibodies against PEPCK recognized polypeptides in electrophoresed samples of cell-free extracts from only non-green phytop lankton and macrophytic Phaeophyta while antibodies against phosphoenolpyru vate carboxylase (PEPC) recognized polypeptides in samples of only chloroph ytes. This supports the hypothesis that PEPCK is the dominant enzyme in LIC F processes in chromophytes while PEPC is the enzyme responsible for non-ph otosynthetic processes in the chlorophytes. The enzyme PEPCK was immune-loc alized in the chloroplasts of the diatom Skeletomema costatum and the kelp Laminaria setchelli which differs from the localization of the enzymes in m ost vascular plants. While LICF processes occur in the cytoplasm of most va scular plants, the results of this study suggest that in marine chromophyte s, LICF processes are catalyzed in tile chloroplasts and that the now of ca rbon varies between these groups of autotrophs.