Iron-binding by macromolecular components of human gastric juice
Swain, C.H.; Glass, G.B.
Journal of Laboratory and Clinical Medicine 81(5): 719-732
1973
ISSN/ISBN: 0022-2143 PMID: 4698659 Document Number: 59708
Fe binding capacity was for human gastric juice after stimulation with histamine 19.1, reconstituted lyophilized human juice 8.71, dog chondroitin sulphate A 5.53 and triple crystalline pig pepsin 22.81 mu g/mg. After separation and refractionation, glycoprotein fractions of human gastric juice eluted at different NaCl concentrations had binding capacities of 10 and 10.12 mu g/mg for blood group type of glycoproteins, 9.86 to 10.71 mu g/mg for sialoglycoproteins and 9.95 mu g/mg for sulphated glycoproteins. Complexing of Fe with buffer was found in some instances even in the absence of a protein binder. When acetone was used to precipitate total gastric glycoproteins the amount of Fe kept in solution by gastric juice at pH 8 was at least 10 times that precipitated from the same supernatant at pH 2. Equilibration dialysis of human gastric juice in water against 59FeCl3 bound to concentrated gastric juice at pH 2 and 59FeCl3 alone in different buffers showed no specific component having electrophoretic mobility of the known macromolecules of gastric juice. Electrophoresis of 59Fe previously bound to gastric juice and eluted from Sephadex G-150 as a single peak showed independent mobility for the 59Fe, separate from the excluded protein peak. The Fe 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 reduced Fe binding capacity of gastric juice, suggesting a role for sialic acid terminal groups in Fe binding.