PURIFICATION AND PARTIAL CHARACTERIZATION OF THE CYANOPLAST GLUCOSE-6-PHOSPHATE-DEHYDROGENASE IN CYANOPHORA-PARADOXA

NADP-dependent enzyme activity of Glucose-6-phosphate-dehydrogenase (G 6PDH: E.C.1.1.1.49) has been detected in a significant amount (by spec trophotometry) within both cell compartments of Cyanophora paradoxa, w ithin the cytosol and the cyanoplast. The cyanoplast enzyme shows a pH optimum of 7.8 (in crude cyanoplast extracts) and is precipitating be tween pH 4.5 to 5. It was enriched about 1800 fold by a three step pur ification procedure (DEAE-Sephadex A25, Cibachron Blue 3GA-Agarose and Mono Q) with 17% yield of the activity of the crude extract (of isola ted cyanoplasts) and with 120 U/mg protein as the final specific activ ity of the purified enzyme. The apparent molecular mass of the monomer ic form is 59 kDa (estimated by SDS-PAGE). Native PAGE shows two oligo meric forms for the enzyme activity: a dimeric (ca. 135 kDa +/- 10 kDa ) and a tetrameric (ca. 285 kDa +/- 25 kDa). The product seems to be N -terminally blocked.