Cobalamin R binder as a possible model molecule for glycoprotein study in cystic fibrosis

Human haptocorrin in hepatocellular carcinoma

This study aimed to determine whether haptocorrin (HC), a vitamin B12 binder, is stored in hepatic cells and whether this storage is modified by hepatic carcinogenesis. It was carried out using immunohistochemistry on different liver tissues (normal liver and steatosis, N = 22; cirrhosis, N = 13; and hepatocellular carcinoma, N = 31). No significant immunostaining of HC was detected in noncancerous biopsies with the exception of in one case of cirrhosis. Hepatocellular carcinoma (HCC) sections showed a weak to moderate cytoplasmic staining of cancerous cells (93% of cases) and of noncancerous hepatocytes surrounding the tumor (95%) of cases. Sections with pseudoglandular structures showed a moderate to strong staining of their secretion products. These results and previous studies would seem to confirm the hypothesis that the raised HC serum level observed in HCC is due both to the increased hepatic synthesis of HC and to a decreased uptake by the liver of the particular isoform of this glycoprotein present in the serum of HCC patients.

Clinical applications of electrophoresis of human salivary proteins

Human salivary proteins have been studied by electrophoresis in denaturing and non-denaturing polyacrylamide gel electrophoresis (PAGE) as well as by isoelectric focusing (IEF) and two-dimensional procedures, and the clinical applications of this have been reviewed. Whilst non-denaturing PAGE is useful in studying polymorphisms, sodium dodecylsulphate PAGE appears to be otherwise preferable. Immobilized pH gradients containing carrier ampholytes (CAs) give better resolution than CA-based IEF and overcome the problems of cathode drift and loss of basic material. Proline-rich proteins stain poorly with conventional procedures and special techniques are necessary. In clinical studies, findings must be viewed over and above the large number of polymorphisms which occur normally. Studies relating salivary protein and peptide profiles to dental caries susceptibility are encouraging. Specific protein abnormalities have been associated with connective tissue disorders and could form the basis of new non-invasive diagnostic procedures. Protein differences associated with cystic fibrosis and diabetes mellitus, however, merit reinvestigation with the new procedures now available. Detection of HIV antigens in saliva is a new area of research. In the light of new techniques available and new information which has arisen from DNA studies, future prospects for the clinical applications of electrophoresis of saliva look good.

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.

Unsaturated B12-binding proteins in amniotic fluid of cystic fibrosis-affected foetus

The authors hypothesized the possibility of quantitative or qualitative abnormalities of amniotic fluid B12-binding proteins in cystic fibrosis. Seven cystic fibrosis and 59 normal amniotic fluids sampled between 17.5 and 18.5 gestational weeks were studied by radioimmunogel filtration, radioisotope technique, and isoelectric focusing chromatography. In normal amniotic fluid there was an increase of unsaturated B12-binding capacity from 16 to 41 weeks of gestation. There was no statistically significant difference in unsaturated B12-binding capacity, molecular weights and isoelectric points of haptocorrin, transcobalamin 2, and intrinsic factor between cystic fibrosis and normal amniotic fluid. Cobalamin-binding proteins study cannot help in the antenatal diagnosis of cystic fibrosis.