CHLAMYDOMONAS-REINHARDTII NADP-LINKED GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE CONTAINS THE CYSTEINE RESIDUES IDENTIFIED AS POTENTIALLY DOMAIN-LOCKING IN THE HIGHER-PLANT ENZYME AND IS LIGHT-ACTIVATED

The chloroplastic glyceraldehyde-3-P dehydrogenase (EC 1.2.1.13) of th e green alga Chlamydomonas reinhardtii is reductively light activated. Homology modeling indicates that the only potential disulfide-forming cysteine residues in this enzyme are the same cysteine residues sugge sted to be responsible for redox-sensitivity of the higher plant enzym e (Li D, Stevens FJ, Schiffer M and Anderson LE (1994) Biophys J 67: 2 9-35). Apparently, the three additional cysteines in the higher plant enzyme are not necessary for light activation. The putative regulatory cysteines are juxtaposed across the domain interface and when oxidize d will crosslink the domains. This would be expected to interfere with interdomain movement and catalysis. This is the first report of reduc tive light activation of this enzyme in a green alga.