Blocking of Hog Intrinsic Factor by Human Gastric Juice and Certain Mucopolysaccharides, Including Blood Group Substance*

Intrinsic factor can bind vitamin B12 and simul- taneously attach to receptors on liver or small in- testine in a calcium-dependent manner (1).There appears to be a stoichiometric relationship between the receptors, intrinsic factor and vitamin B12 (2).This report, previously presented in preliminary form (3), is concerned with blocking of the re- ceptor sites for hog intrinsic factor by human gastric juice and certain mucopolysaccharides, in- cluding blood group substance. MATERIALS AND METHODSGastric juice was collected before and after insulin stimulation of fasting patients.A Dreiling tube (4) was used to avoid contamination with saliva and bile.1 Gas- tric juices were pooled according to the blood group of the donors, centrifuged, neutralized with NaOH (20 per cent), and frozen.Saliva was collected from blood group A-secretors and filtered through gauze.Comnmercial preparations of blood grotp A and B suib- stances 2 were obtained from large pools of equine and porcine gastric mucosa after enzymatic digestion and alcohol precipitation.Degraded blood group A and B polvsacchlarides ('P-1 fraction") were prepared from the commercial prepara- tions (Merck) by mild acid hydrolysis with dilute HCl, pH 2.0, at 1000 C for 2 hours, followed by dialysis for 4 days against 4 changes of tap water.This treatment splits off fucose and certain oligosaccharide side chains, some of which determine blood group specificity, but * This investigation was supported in part by Grant A-2684, National Institute of Arthritis and Metabolic Diseases, Bethesda, Md.