Purification of a Complex of Alkaline Fructose 1, 6-Bisphosphatase and Phosphoribulokinase from Rhodospirillum rubrum

Two enzymes of the reductive pentose phosphate cycle, alkaline fructose 1,6-bisphosphatase and phosphoribulokinase, have been isolated and purified as a single complex from Rhodospirillum rubrum.During purification procedures involving ammonium sulfate precipitation and column chromatography with both DEAE-cellulose and Sephadex, the ratios of activity of one enzyme to that of the other remained approximately the same.The pure complex appeared as a single band on polyacrylamide gels, and the activities of the two enzymes showed the same profiles on an isoelectric focusing column.No other enzyme of the reductive pentose phosphate cycle could be detected in the complex.The complex was unstable, so that after 48 hours the activity of phosphoribulokinase was reduced by 80% and that of fructose 1,6-bisphosphatase by 50%.This loss of activity was accompanied by the appearance of two bands on the polyacrylamide gels.The most widespread series of reactions responsible for the fisat,iou of carbon dioside into the early products of photosynthesis are those that constitute the reductive pentose phosphate cycle (the Calvin cycle).Recent,ly, there has been increasing interest in the mechanism by which this cycle is regulated (1).Essent'ially, there have been two approaches to the problem of control of the Calvin cycle.The first involves "physiological" studies of intact organisms or intact rhloroplasts (2-5).The second approach has been the isoltition of enzymes believed to be important in the regulation of l)llotosVlltltetic' carbon dioxide assimilation and attempbs to affect the activity of such enzymes in ways that might relate to their control in z%vo (6-14).