Leaf Cytosolic Fructose-1,6-bisphosphatase

Leaf cytosolic fructose-1,6-bisphosphatase (FBPase), partially purified from both spinach (Spinacia oleracea, var Hipack) and peas (Pisum sativum, var Progress No. 9), is reversibly inactivated by exposure to low temperature. Thus, even though assays were conducted at 22 degrees C, samples incubated at 0 to 12 degrees C had greatly reduced activity relative to controls maintained at 22 degrees C. Following incubation at 22 degrees C prior to assay, the inactivated samples regained their initial activity. Chloroplast FBPase, by contrast, was unaffected by low temperature treatment. This feature as well as lack of a response of cytosolic FBPase to thioredoxins f or c(f) and to chloroplast FBPase antibody indicate that the FBPase isozymes of leaves are different proteins.