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.
PHOTOSYNTHETIC PIGMENTS OF SYMBIOTIC DINOFLAGELLATES (ZOOXANTHELLAE) FROM CORALS AND CLAMS