Carbon fixation by the peculiar marine diatom Haslea ostrearia

During batch culture of Haslea ostrearia the highest carbon (C-14) fixation rate was found in vivo in cells that did not accumulate the blue pigment m arennine (green form). This fixation rate decreased concomitantly with the accumulation of marennine. In vitro, no phosphoenolpyruvate carboxylase (PE PC) activity was detected, but nearly equivalent activities of ribulose-1,5 -bisphosphate carboxylase (RuBPC) and phosphoenolpyruvate, carboxykinase (P EPCK) were found in the green form. However, the activity of RuBPC was lowe r than that of PEPCK during marennine accumulation. In vitro carboxylase ac tivities were strongly inhibited by the addition of a marennine extract. A full description of this inhibition could not be confirmed within the cells because marennine accumulates in small cytoplasmic vesicles.