PHOSPHOENOLPYRUVATE CARBOXYKINASE ACTIVITY IN <i>ASCOPHYLLUM NODOSUM</i> (PHAEOPHYCEAE)¹

Abstract

ABSTRACT PEP‐dependent 4 CO 2 ‐fixation by extracts of Ascophyllum nodosum (L.) Le Jol. is reported. The carboxylation of PEP is Mn 2+ dependent and ATP is shown to be a product. IDP was found to be less efficient as a phosphate acceptor than ADP and 3‐mercaptopicolinic acid inhibited the carboxylation reaction. Extracts decarboxylated OAA only in the presence of ATP and had high activities of MDH and GOT. This evidence, together with the probable absence of PEPC, PEPCTrP, and PC in A. nodosum extracts, favors the view that PEPCK is responsible for the light‐independent CO 2 ‐fixation observed in this alga.