The F1-ATPase β-subunit is the putative enterostatin receptor

It has been suggested that the F-1-ATPase beta-subunit is the enterostatin receptor. We investigated the binding activity of the purified protein with a labeled antagonist, beta-casomorphin(1-7), in the absence and presence of cold enterostatin. I-125-beta-casomorphin(1-7) Weakly binds to the rat F-1-ATPase beta-subunit. Binding was promoted by low concentrations of cold enterostatin but displaced by higher concentrations. To study the relationship between binding activity and feeding behavior. we examined the ability of a number of enterostatin analogs to affect beta-casomorphin(1-7) binding to the F-1-ATPase beta-subunit. Peptides that suppressed food intake promoted beta-casomorphin(1-7) binding whereas peptides that stimulated food intake or did not affect the food intake displaced P-casomorphini-I binding. Surface plasmon resonance measurements show that the beta-subunit of F-1-ATPase binds immobilized enterostatin with a dissociation constant of 1-50 nM, where no binding could be detected for the assembled F-1-ATPase complex. Western blot analysis showed the F-1-ATPase beta-subunit was present on plasma and mitochondrial membranes of rat liver and amygdala. The data provides evidence that the F-1-ATPase beta-subunit is the enterosatin receptor and suggests that enterostatin and beta-casornorphin(1-7) bind to distinct sites on the protein. (C) 2004 Elsevier Inc. All rights reserved.