Biological action of phosphonate analogs of fructose 2,6‐bisphosphate on enzymes from higher plants

Two analogs of fructose 2,6‐bisphosphate have been prepared, in which the phosphoryl group on the second carbon is replaced by a methylphosphonoyl or a phosphonoyl group. Both inhibited spinach leaf cytosolic fructose‐1,6‐bisphosphatase and activated potato tuber pyrophosphate:fructose‐6‐phosphate phosphotransferase. Their relative effectiveness depended on the enzyme, revealing differences in the fructose 2,6‐bisphosphate binding sites on the two enzymes. Their relative effectiveness and their binding constants were the same when pyrophosphate:fructose‐6‐phosphate phosphotransferase was assayed in the forward and in the reverse direction. It is concluded that pyrophosphate:fructose‐6‐phosphate phosphotransferase possesses one type of fructose 2,6‐bisphosphate binding site, and catalysis is modified in parallel in both directions as the activator concentration is altered. These results led to the reinterpretation of the role of pyrophosphate:fructose‐6‐phosphate phosphotransferase and fructose 2,6‐bisphosphate in higher plants.