IDENTIFICATION OF A POTENTIAL REDOX-SENSITIVE INTERDOMAIN DISULFIDE IN THE SEDOHEPTULOSE BISPHOSPHATASE OF CHLAMYDOMONAS-REINHARDTII

In the simulated three-dimensional structure of the Chlamydomonas rein hardtii sedoheptulose bisphosphatase (EC 3.1.3.37) there are two cyste ine residues close enough to one another to form a redox-sensitive dis ulfide bond which would cross-link the nucleotide and carbon substrate domains. Examination of the redox modulation of this sedoheptulose bi sphosphatase confirms that it resembles the higher plant enzyme in bei ng activated by reduction. In the wheat and Arabidopsis enzymes, for w hich there is sequence information and which, like the Chlamydomonas e nzyme, can be modeled, both redox-sensitive Cys residues appear to be located on the regulatory nucleotide-binding domain. Apparently differ ent Cys residues are involved in modulation in the algal and higher pl ant sedoheptulose bisphosphatases.