Urinary autoantibodies against intrinsic factor in pernicious anaemia patients.

In radioimmunoassay seven concentrated urines of penicious anaemia (PA) patients were positive for intrinsic factor (IF). Four were studied by gel filtration. Two contained both binding and blocking antibodies against IF, one had only blocking antibodies and one lacked both types of antibodies. The antibodies were mainly of the IgG-type. No such antibodies were found in the urine of a healthy person. None of the urines studied contained enough protein to be classified as proteinuric. Not until the interferences of the autoantibodies in the IF assay can be eliminated is the assay of value in the diagnosis of PA.

Concentration and physicochemical characterisation of unsaturated cobalamin binding proteins in amniotic fluid.

Indirect evidence for the presence of intrinsic factor in amniotic fluid has been provided recently, using either a radioisotope binding assay or a radioimmunoassay. We have determined the unsaturated cobalamin binding capacity and the physicochemical properties of the 3 cobalamin binding proteins in 59 amniotic fluids using radioisotope binding assay, gel filtration and isoelectrofocussing. A good correlation with gestational age was found for the total unsaturated Cbl binding capacity (r = 0.735) and for the concentration of unsaturated haptocorrin (r = 0.746), but not for the concentration of unsaturated intrinsic factor (r = 0.003). When their binding capacities were expressed as a percentage of the total unsaturated Cbl binding capacity, the percentage of intrinsic factor, transcobalamin II and transcobalamin III (the less acidic fraction of haptocorrin) decreased and the percentage of haptocorrin increased in function of gestational age. The physicochemical properties of intrinsic factor in amniotic fluid were close to those in gastric juice: the molecular mass was estimated to 49,200 +/- 4,900 Da (n = 24) in Sephacryl S 300 gel filtration, the cobalamin-protein complex was resolved in 2-6 isoproteins isoelectric at a pH range of 4.6-5.8 and with a mean isoelectric point of 5.18 +/- 0.16 (n = 5) in isoelectrofocusing and it crossreacted with anti-intrinsic factor autoantibodies (from a Biermer anaemia serum). Amniotic fluid collected at 13 wk of gestational age was found to contain intrinsic factor and haptocorrin with less acidic isoproteins than those usually observed in gastric juice and serum. This could indicate that sialic acid is less involved in the composition of the carbohydrate core of cobalamin binding glycoproteins in this period of the gestational age than later on and that cobalamin binding proteins have mainly a foetal origin.

Effect of glycosidases and proteinases on cobalamin binding and physicochemical properties of purified saturated haptocorrin and intrinsic factor.

The effect of exoglycosidase, N-glycanase, trypsin and chymotrypsin was studied on the binding capacity and physicochemical properties of intrinsic factor and of haptocorrin using Superose 6 gel filtration. Intrinsic factor was purified as recently described by us. Haptocorrin was purified 6000-fold from human saliva using thermolabile affinity chromatography and high-performance cationic exchange chromatography with a specific activity of 20.6 nmol of cobalamin (Cbl) per mg protein and a yield of 44.7%. Exoglycosidases provoked a decrease of 54.3 and 78.2% of the Cbl binding capacity of haptocorrin and intrinsic factor, respectively. The sequential incubation of haptocorrin and intrinsic factor wit exoglycosidases and proteinases provoked a decrease of, respectively, 100 and 92.7% of their Cbl binding capacity, whereas the incubation with proteinase decreased the Cbl binding capacity of, respectively, 67.9 and 7.9%. The result of the incubation of [3H]intrinsic factor or [3H]haptocorrin with chymotrypsin and trypsin gave, respectively, no change in the elution position and a shift corresponding to a decrease of 50% of the estimated molecular mass. The estimated molecular mass of Cbl-intrinsic factor and of Cbl-haptocorrin decreased, respectively, to 57.1 kDa and to 88.1 kDa after incubation with exoglycosidases. It was concluded that (1) the carbohydrate core of intrinsic factor protects the whole protein whereas the carbohydrate core of haptocorrin protects only half part of the protein and (2) the carbohydrates are implicated in the formation of the cobalamin binding site of haptocorrin and intrinsic factor.

Cobalamin-binding proteins in human urine: identification and quantitation.

The urinary cobalamin (Cbl) binders were examined by gel filtration of concentrated urine on Sephadex G-200, alone and together with immunoglobulins against human Cbl binders. The 11 urine specimens from 10 persons studied had a free Cbl-binding capacity of 0.76 to 30.0 pmol/L (mean 6.6 pmol/L). Gel filtration with buffer preventing association of the Cbl binders gave peaks with elution volumes characteristic of serum transcobalamin and haptocorrin. When concentrated urine specimens were run together with immunoglobulins, the findings confirmed the presence of haptocorrin and transcobalamin and, in addition, of intrinsic factor. The presence of intrinsic factor was confirmed by incubating urine with an ion exchanger gel and by showing that an eluate of the gel reacted with the corresponding immunoglobulin. Part of the urinary intrinsic factor detected by radioimmunoassay was able to bind 57Co-Cbl; the rest appeared to be saturated with endogenous Cbl and possibly partly incapable of binding Cbl. All the free Cbl-binding capacity of urine concentrate could be blocked with adenine cyanocobamide, but only half with cobinamide; cobinamide blocked all the urinary haptocorrin but only part of the transcobalamin and none of the intrinsic factor eluted from the ion exchanger gel.

Intrinsic factor in human amniotic fluid as determined by radioimmunoassay.

The intrinsic factor (IF) concentration in 55 human amniotic fluid specimens was determined by radioimmunoassay (RIA). The antiserum was produced by immunizing rabbits with the cobalamin-IF complex isolated from human gastric juice. The median concentration of IF was 0.17 nmol/l and the extreme values less than 0.07-2.51 nmol/l. Three specimens with a clearly elevated level (0.96, 1.11 and 2.51 nmol/l) were observed. The highest value was associated with a fetal malformation, viz. obstruction of the proximal gut. There was no evident correlation between the concentration of IF in amniotic fluid and gestational age.