Iron-binding by macromolecular components of human gastric juice.

Abstract

Abstract In evaluating the role of human gastric juice and its macromolecular components in iron-binding and protecting iron salts from precipitation at an alkaline pH, we found the phenomenon to be nonspecific. Various fractions of sulfated and nonsulfated glycoproteins from human gastric juice, dog chondroitin sulfate A, and triple crystaline hog pepsin have manifested similar iron-binding effects. Complexing of iron with buffer was noted in some instances, even in the absence of a protein "binder." The amount of iron kept in solution by gastric juice at pH 8 and claimed to represent iron bound to glycoprotein was at least 10 times higher than that precipitated from the same supernatant by acetone at pH 2, procedure known to precipitate total glycoproteins. Equilibration dialysis of human gastric juice in water against 59 FeCl 3 "bound" to concentrated gastric juice at pH 2, and 59 FeCl 3 alone in various buffers of a wide range of pH's and ionic strength revealed no specific component having electrophoretic mobility of the known macromolecules of gastric juice. Electrophoresis of 59 Fe previously bound to gastric juice and eluted from Sephadex G-150 as a single peak revealed independent mobility for the 59 Fe, separate from the excluded protein peak. The iron "bond" which may form in alkaline pH is weak, and is probably of ionic nature, being readily dissociable by electrophoresis, detergent action, or alteration in ionic strength and pH. Neuraminidase digestion caused considerable reduction in iron-binding capacity of gastric juice, suggesting a role for sialic acid terminal groups in iron binding.