REDOX SENSITIVITY AND LIGHT-MODULATION OF ENZYME-ACTIVITY IN THE RHODOPHYTES GRACILARIA-TIKVAHIAE AND CHONDRUS-CRISPUS

One of the cysteine residues believed to be necessary for reductive li ght activation is lacking in the only red algal NADP-linked glyceralde hyde-3-P dehydrogenases for which sequences are available, namely Grac ilaria verrucosa (Hudson) Papenfuss and Chondrus crispus Stackhouse. C onsistent with the mechanism of light modulation proposed for this enz yme, which involves reduction of domain movement-restricting disulfide bonds, it is not reductively activated in Chondrus crispus extracts, and it is not light-activated in whole cells or dithiothreitol (DTT) a ctivated in extracts of the North American species Gracilaria tikvahia e McLachlan. Fructosebisphosphatase and glucose-6-P dehydrogenase, two enzymes for which sequence information from these algae is not yet av ailable, are both activated in crude extracts by DTT treatment, but on ly fructosebisphosphatase is light-activated in intact Gracilaria.