Role of Aldolase in Photosynthesis. I. Enzyme Studies With Photosynthetic Organisms With Special Reference to Blue-Green Algae.

Hexose formiiation during photosynthesis has been presumed to occur by means of the reductive pentose phosphate cycle (3). An integral part of this cycle is the condensation of two molecules of triosephosphate to yieldl fructose-1,6-diphosphate (FDP) in a reaction catalyzed by aldolase. In support of aldolase participating in photosynthesis, Tewfik and Stumpf (35) showed that aldolase was present in photosynthetic tissues of all the higher plants which they examined. There is, however, evidence that this enzyme is absent or very low in some photosynthetic organismiis. Jacobi ( 11 ) noted the absence of aldolase in four species of red algae. Szymona and Doudoroff (33) could find only traces of the enzyme in Rhodopseudmiionas spheroides. Richter (24, 25) has reporte(l that the enzyme cannot be detected in the bluegreen alga, Anacystis nidulans, or in a strain of Rhodopseudonmonas spheroides. Peterkofsky and Racker (20) have recently determined the activities of several enzymes of the reductive pentose phosphate cycle in spinach, Euglena, and in a high temperature and a low temperature strain of Chlorella. Their data showedl that in all four organisms transaldolase, sedoheptulose-1,7-diphosphatase and fructose-1,6-diphosphatase were present in insufficient amounts to support the rate of CO, fixation by intact cells. Furthermore, aldolase was also low in both Euglena and the low temperature strain of Chlorella. The present study is an attempt to assess the role of aldolase in photosynthesis. In the first paper of this series, aldolase and enzymes associated with the reductive pentose phosphate cycle have been (letermined in various organisms, with special reference to the Cyanophyceae algae.