9] Solubilization of the receptor for intrinsic factor—B12 complex from guinea pig intestinal mucosa

Abstract

Publisher Summary This chapter discusses an overview of solubilization of the receptor for intrinsic factor-B 12 complex from guinea pig intestinal mucosa. The absorption of dietary vitamin B 12 from the intestine in many animal species requires the presence of intrinsic factor (IF), a glycoprotein secreted by the gastric mucosa. Normally, this protein is produced in large excess over actual requirements and is rarely a limiting factor in absorption. In vitro studies employing everted intestinal sacs, mucosal homogenates, and microvillous membranes prepared from the distal, but not the proximal, small bowel show uptake of IF-B 12 complex in the presence of a physiologic pH and calcium ions. The implication of this is that a receptor for IF-B 12 complex exists at the surface of the ileal cell. This chapter describes solubilization of guinea pig ileal mucosal homogenates employing the detergent Triton X-100. A particle-free solution was obtained that contained all the IF-B 12 receptors estimated to be present on the starting intestinal membranes. It is expected that better quantitation of IF- B12 receptor will help investigators to elucidate the mechanisms of B 12 absorption and malabsorption. The method employed for assaying and quantitating this solubilized receptor is also described in the chapter.