Glucose-6-phosphate dehydrogenase (Zwischerfferment) and 6-phosphogluconate dehydrogenase, first studied in y e a s t by Warburg and his coworkers (1, 2), have since been found in a number of cells and tissues. These have received extensive study because they provide a pathway for formation of pentose phosphate from hexose phosphate and because of the possibility that oxidation of glucose-6-phosphate by this means may provide energy for function. (See references 3--6.)The present experiments deal with the occurrence, the properties, and the relation to over-all metabolism of these two enzymes in eggs of the sea urchin, Arbacia punctulata; they are part of a general survey of the enzymes of Arbacia eggs (7).
Experimental MethodsThe eggs were obtained and handled as previously described (8, 9). Homogenates were prepared as before (9), except that citrate was omitted from, and 0.004 ~ ethylenediamine tetraacetic acid included in, the homogenizing medium to minimize breakdown of the echinochrome granules; the homogenates were a light orange-pink and the supernatant fractions obtained therefrom by centrifugation at 20,000 g for 30 minutes were clear and of a straw yellow color. The homogenates and other fractions to be tested were kept at ice water temperature; full activity was retained for 6 to 8 hours; 20 to 40 per cent of the initial activity of the homogenate or supematant fractions was lost by a single freezing and thawing; this procedure appeared relatively more damaging to the phosphogluconate dehydrogenase than to glucose-6-phosphate dehydrogenase. The values recorded in the tables and figures were calculated by use of the conversion factors previously derived (10).The sources of the special reagents were: Sigma Chemical Company, triphosphopyridine nucleotide (TPN), 83 per cent purity (assayed by yeast Zwischenferment), barium glucose-l-phosphate, and yeast Zwischenferment (lot No. 54-137, virtually free of phosphogluconate dehydrogenase);