Different involvement for aldolase isoenzymes in kidney glucose metabolism: Aldolase B but not aldolase A colocalizes and forms a complex with FBPase

The expression of aldolase A and B isoenzyme transcripts was confirmed by RT-PCR in rat kidney and their cell distribution was compared with characteristic enzymes of the gluconeogenic and glycolytic metabolic pathway: fructose-1,6-bisphosphatase (FBPase), phosphoenol pyruvate carboxykinase (PEPCK), and pyruvate kinase (PK). We detected aldolase A isoenzyme in the thin limb and collecting ducts of the medulla and in the distal tubules and glomerula of the cortex. The same pattern of distribution was found for PK, but not for aldolase B, PEPCK, and FBPase. In addition, co-localization studies confirmed that aldolase B, FBPase, and PEPCK are expressed in the same proximal cells. This segregated cell distribution of aldolase A and B with key glycolytic and gluconeogenic enzymes, respectively, suggests that these aldolase isoenzymes participate in different metabolic pathways. In order to test if FBPase interacts with aldolase B, FBPase was immobilized on agarose and subjected to binding experiments. The results show that only aldolase B is specifically bound to FBPase and that this interaction was specifically disrupted by 60 microM Fru-1,6-P2. These data indicate the presence of a modulated enzyme-enzyme interaction between FBPase and isoenzyme B. They affirm that in kidney, aldolase B specifically participates, along the gluconeogenic pathway and aldolase A in glycolysis.