THE COMPABILITY WITH ENZYME-ACTIVITY OF UNUSUAL ORGANIC OSMOLYTES FROM MANGROVE RED ALGAE

The effects of organic osmolytes synthesised and accumulated by red al gae from mangrove habitats were investigated on the in vitro activitie s of two major enzymes, one of the citric acid cycle (malate dehydroge nase, MDH) and one of the oxidative pentose phosphate pathway (glucose -6-phosphate dehydrogenase, G6PDH). These enzymes were extracted from the mangrove algae Bostrychia tenella, Caloglossa leprieurii, Catenell a nipae and Stictosiphonia hookeri. In each case, activity of the enzy mes was inhibited with increasing NaCl concentrations up to 600 mM. In contrast, equimolar concentrations of mannitol (the major osmolyte in C. leprieurii), sorbitol (the major osmolyte in B. tenella and S. hoo keri) and a heteroside mixture (of which floridoside is the major osmo lyte in C. nipae) did not inhibit enzyme function. Dulcitol, the secon d most important organic osmolyte in B. tenella, exerted no negative e ffect at its maximum solubility of 180 mM on the salt-sensitive MDH. T hese data are all consistent with the proposed function of these organ ic compounds as compatible solutes.