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Biomedical subjects

B de Bernard

Publications and source records attributed to B de Bernard.

33 records · Page 2Linked to original sources
PubMed1981

Ca2+-binding studies of the phosphoprotein from rat-incisor dentine.

Rat incisor dentine was demineralized and extracted with 0.25 M EDTA containing protease inhibitors. The extract was purified by chromatography on DEAE-cellulose and sulfonated polystyrene. The Ca2+-finding properties of the phosphoprotein were studied by dynamic dialysis and by using a Ca2+-selective electrode. Two different binding sites were detected with Kd = 0.9 X 10(-7) M and 1.1 X 10(-5) M and displaying a Ca2+-binding capacity of 127 and 176 mol bound Ca2+/mol protein, respectively, assuming a molecular weight of 30 000. Upon enzymatic dephosphorylation of the phosphoprotein, the highest affinity sites disappeared and those with the lowest affinity were reduced. The optimum for Ca2+ binding by the phosphoprotein occurred at pH 8.2. The specificity of the Ca2+ ion interaction with the phosphoprotein was investigated by studying the competitive nature of other divalent and monovalent cations. It was found that Ca2+ ions were to a large extent displaced from the phosphoprotein by other cations in physiological concentrations.

Animals↗
PubMed1980

Influence of calcium depletion on medullary bone of laying hens.

Medullary bone of birds maintained on a low-calcium diet represents a good model to study modifications of matrix composition in calcified tissue undergoing intense formation and resorption. The composition of the bone matrix during the low-calcium diet has been analyzed by both chemical and histological techniques. Sixty White Leghorn pullets 1 year old were used for the experiment. Fifteen birds served as controls and were killed on day zero; the remaining birds were placed on a calcium-deficient diet (0.13% calcium) and sacrificed after 4, 7, and 12 days of treatment in groups of 15. Serum levels of calcium, PTH, and estrogens were also measured. Chemical analysis of the samples were made for total nitrogen, hydroxyproline, hexosamine, hexoses, calcium, and phosphorus. Collagen and proteoglycans of the matrix of medullary bone of the egg-laying hens were found to be affected by the low-calcium diet. They either increased or decreased during the experiment but never in parallel. The increment of serum PTH is considered responsible for the variations in the amount of collagen. The effects of this hormone are magnified by the fall of serum estrogens as shown also by variations in the amounts of noncollagenous protein. In the late phase of the diet the matrix is represented by poorly calcified osteoid tissue rich in noncollagenous protein, i.e., proteoglycans and glycoproteins.

Animals↗
PubMed1980

Cation binding by the rat-incisor-dentine phosphoprotein. A spectroscopic investigation.

Nuclear magnetic resonance and electron paramagnetic resonance spectroscopy have been used to quantify metal binding to the phosphoprotein extractable from demineralized rat incisor dentine. Paramagnetic cation probes enable identification of the metal binding sites. Cations are able to diffuse across the protein surface while forming a relatively long-lived metal-phosphoprotein complex. The ability of the protein to sequester surface-mobile Ca(II) is discussed in terms of its ability to act as a possible nucleation site for the initial localization of Ca(II) within the dentine matrix.

Animals↗
PubMed1980

Ca2+-binding glycoprotein in avian bone induced by estrogen.

The discovery in calcifying cartilage of a glycoprotein, endowed with high calcium affinity and alkaline phosphatase activity, has prompted the investigation of the presence of this compound in other calcified tissues. From medullary bone, a tissue which is highly mineralized under estrogen stimulus, a glycoprotein has been extracted which had the properties described. Besides the high calcium affinity (KD = 10(-7)M), this protein shows phosphatase activity and rate of hydrolysis of ATP, GTP and pyrophosphate was measured. Analysis of the chemical composition of the matrix of the medullary bone indicates that proteoglycans are present in large amounts. The calcium binding glycoprotein appears to be a compound present in different calcified tissues.

4-Nitrophenylphosphatase↗
PubMed1979

Enzymatic properties of the Ca2+-binding glycoprotein isolated from preosseous cartilage.

The Ca2+-binding glycoprotein isolated from preosseous cartilage shows also alkaline phosphatase activity. The purification procedure indicates that the enzyme is inhibited in crude extract and conceivably in the intact tissue; the activity may be controlled by the proteoglycans present in the matrix. Other substrates are hydrolyzed by the purified enzyme in addition to p-nitrophenylphosphate; the highest specific activity was measured with ATP and pyrophosphate (PPi) at pH 7.5 and 9.0 Mg2+ induces an activation of ATP and PPi hydrolysis; Ca2+ activates hydrolysis of ATP but inhibits that of PPi. The glycoprotein shows also transphosphorylase activity, L-serine being the best phosphate acceptor. The release or transfer of Pi catalyzed by the glycoprotein can be an important step in calcium phosphate precipitation.

Alkaline Phosphatase↗
PubMed1975

Properties of beta-glucuronidase activity in human synovial fluid.

The purpose of the present study was to evaluate the properties of beta-glucuronidase (EC 3.2.1.31) in human synovial fluid. It was shown to have a pH requirement of 5.0 and a KM value of about 8.0 - 10(-3) M using phenolphthalein beta-glucuronide as the substrate. At low substrate concentration an endogenous inhibitor is demonstrable. The inhibition is of the competitive type and is removed by proteolytic digestion of synovial fluid, whereas hyaluronidase digestion and addition either of Triton X-100 or of various salts to the assay mixture, are ineffective. The possibility that the inhibitor is a protein from serum is discussed.

Animals↗
PubMedDate not supplied

Proton MR spectroscopy in quantitative in vivo determination of fat content in human liver steatosis.

To demonstrate that the lipid volume fraction in liver steatosis can be accurately estimated with in vivo hydrogen-1 magnetic resonance (MR) spectroscopy, the authors developed a calibration procedure based on in vitro MR spectroscopy of lipid extracts from steatotic liver specimens. The lipid volume fractions determined with the calibration procedure were compared with the results of histomorphometry and with calibrated computed tomographic (CT) data. The volume fraction of fat determined with MR spectroscopy was in good agreement with the CT results, whereas histomorphometry underestimated the amount of hepatic fat. The results indicate that determination of the fat volume fraction in steatotic liver can be achieved noninvasively with MR spectroscopy.

Adult↗
PubMedDate not supplied

Glycoproteins in the local mechanism of calcification.

Glycoproteins in calcifiable matrices appear to play two different roles. As structural components, glycoproteins are associated with proteoglycans of which they share many properties and functions. In particular they are removed before the onset of calcification, therefore unmasking sites of calcium and phosphate deposition. As calcium and/or phosphate binding sites, glycoproteins appear to be associated with the mechanism of calcification. Glycoproteins may aid in transporting calcium and phosphate from points of initial deposition into the relatively inaccessible sites of mineralization. It is possible to assume also a nucleating effect and it cannot be excluded that Ca-binding glycoproteins are components of the "crystal ghosts." Glycoproteins also modulate calcium dependent phosphatase and ATPase activities. The recent discovery of an ATP-driven calcium pump associated with the plasma membrane of chondrocytes and the previous finding of an ATPase activity associated with the cartilage calcium-binding glycoprotein suggest that reduction in ATP content in matrix vesicles may be responsible for the initial deposits of mineral.

Adenosine Triphosphatases↗