A4 glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was purified from the green algaChlamydomonas reinhardtii andwas alsooverexpressed inEscherichia coli. Bothpurified A4 tetramers of recombinant and native GAPDH were characterized for the first time. The pH optimum for both nativeandrecombinant enzymeswas close theresidues involvedincatalysis indicate thatacysteineanda histidinemay take part in catalysis by chloroplast GAPDH, as is the case for glycolytic GAPDH.