Properties of Phosphoenolpyruvate Carboxykinase From Ascophyllum Nodosum (Phaeophyceae)¹

Phosphoenolpyruvate carboxykinase was purified to electrophoretic homogeneity from the brown alga. Ascophyllum nodosum (L.) le Jol. Its molecular mass was 60 kDa as determined by gel filtration. The pH optimum of the carboxylating reaction was 7.9 and the apparent K m for PEP 4 , ADP and HCO 3 ‐ were 0.036, 0.0116 and 50 mol · m ‐3 , respectively. Rates of light and dark carbon fixation are also reported for A. nodosum apices and it is shown that rates of in vitro PEPCK activity would account for the observed rate of dark fixation. The physiological role of PEPCK is discussed in relation to light‐independent carbon fixation.