Activities of enzymes in β-carboxylation reactions and of catalase in cell-free preparations from the symbiotic dinoflagellates Symbiodinium spp. from a coral, a clam, a zoanthid and two sea anemones

Abstract

Cell-free extracts of cultured and freshly isolated symbiotic dinoflagellates, Symbiodinium spp, isolated from the stony coral Montipora verrucosa , the clam Tridacna maxima , the zoanthid Palythoa sp. and the sea anemone Aiptasia pulchella were assayed for the enzyme systems involved in β-carboxylation and photorespiration. Markedly different levels of phosphoenolpyruvate carboxylase (EC 4 . 1 . 1 .31; PEP-case) activity were demonstrated in extracts from the different algae. The activity of PEP-case in the algae from M. verrucosa was highest, being an order of magnitude higher than PEP-case in algae from Palythoa sp. and up to 25-fold higher than that in algae from A. pulchella and T. maxima . The algae from M. verrucosa also exhibited pyruvate-P i dikinase (EC 2 . 7 .9 .1) activity. When these data are combined with previous demonstrations of the existence of NAD malate dehydrogenase and NADP malate dehydrogenase (decarboxylating; ‘malic enzyme’) in these algae, the indications are that they possess functional β-carboxylation enzyme systems. Past demonstrations of the photoassimilation of 14 CO 2 into glycollate by Symbiodinium spp. indicated photorespiration. The demonstration for the first time of activity of catalase (EC 1 . 11 . 1 . 6) when viewed in light of previous demonstrations of other composite enzymes of the photorespiratory pathway (e.g. phosphoglycollate phosphatase, glycollate dehydrogenase), add further confirmation to the disputed existence of a functional photorespiratory system in these symbiotic dinoflagellates.