Search PubMed⌕ Search

Biomedical subjects

H B White

Publications and source records attributed to H B White.

At least 55 records · Page 3Linked to original sources
PubMed1987

Relationship of biotin deposition in turkey eggs to dietary biotin and biotin-binding proteins.

The biotin and biotin-binding protein contents of egg yolk, egg albumen, and hen plasma were determined on eight groups of four turkey hens each that had been fed diets ranging from less than 10 to 3,475 micrograms available biotin per kilogram. Biotin deposition in the yolk was strongly dependent upon available dietary biotin below 100 micrograms/kg. Between 100 and 1,000 micrograms/kg the amount of biotin deposited in the yolk increased slightly and was directly related to and limited by a biotin-binding protein that transferred biotin from the plasma to the yolk. Over the entire dietary range, biotin deposition in yolk was proportional to the total biotin concentration in the plasma. In contrast, biotin deposition in the albumen, which was proportional to dietary biotin, increased several-fold over a very narrow range of plasma biotin concentration (56 to 62 micrograms/L). When dietary available biotin exceeded 160 micrograms/kg, there was more biotin deposited in the albumen than in the yolk. Although the concentration of unbound biotin in plasma is low, it appears to be the component of plasma biotin that is rapidly scavenged by avidin in the oviduct. It seems likely that avidin-bound biotin is available to the turkey embryo.

Animals↗
PubMed1987

Vitamin-binding proteins in the nutrition of the avian embryo.

Nutrients required for the growth and development of an avian embryo must be present when the egg is laid. Many, if not most, of the nutrients in eggs are transferred from the blood plasma of the hen into the yolk of the oocyte as specific nutrient-protein complexes. Egg yolk contains vitamin-binding proteins for thiamin, riboflavin, biotin, cobalamin, retinol, and cholecalciferol. The biochemical details of how these plasma vitamin-protein complexes are recognized by and deposited in the oocyte and subsequently dissociated for use by the embryo are not known. Niacin and ascorbic acid are synthesized by the embryo from other compounds deposited in the egg. Pantothenic acid, which is abundant in the egg, is not bound tightly to a specific protein. Binding proteins for thiamin, riboflavin, biotin, and cobalamin are also present in egg white. Because they are usually not saturated with respect to their ligand, these binding proteins are able to scavenge nutrients and thereby are thought to protect the embryo from infection by microbes that require the ligands. In the albumen of a few species, nutritionally significant amounts of bound riboflavin or biotin are present, suggesting both nutritional and antimicrobial functions for their binding proteins. It is postulated that differences in the amounts of various nutrient-binding proteins correspond to differences in the nutrient contents among the eggs of various species and reflect differences in the nutrient needs of the contained embryos. Mutations that inactivate nutrient-binding proteins arrest development before hatching and are dependent solely on the maternal genotype.

Animals↗
PubMed1986

Riboflavin-binding protein. Concentration and fractional saturation in chicken eggs as a function of dietary riboflavin.

The concentration of riboflavin and riboflavin-binding protein were determined in the plasma, egg yolk and albumen from hens fed a riboflavin-deficient diet (1.2 mg/kg) supplemented with 0, 1, 2, 3, 10 and 40 mg of riboflavin/kg. We observed that the deposition of riboflavin in egg yolk and albumen is dependent on dietary riboflavin and reaches half-maximal values at about 2 mg of supplemental riboflavin/kg. The maximal amount of riboflavin deposited in the yolk is limited stoichiometrically by the amount of riboflavin-binding protein, whereas the maximum amount of riboflavin deposited in albumen is limited by other factors before saturation occurs. The amount of riboflavin-binding protein in yolk and albumen is independent of dietary riboflavin. If there is a specific oocyte receptor for riboflavin-binding protein, it cannot distinguish between the apo and holo forms of the protein. Riboflavin-binding protein is about six times more concentrated in yolk than in plasma.

Animals↗
PubMed1985

Phosphorylation sites in riboflavin-binding protein characterized by fast atom bombardment mass spectrometry.

The capability of fast atom bombardment mass spectrometry for characterization of phosphorylation sites in a tryptic peptide from chicken egg yolk riboflavin-binding protein has been evaluated. The quality of information about molecular weight, amino acid sequence, phosphorylation sites, and microheterogeneity is evaluated as a function of the sign of the ions analyzed, the nature of the counter ions associated with the phosphate substituents, sample matrix, and various instrumental parameters. The intact octaphosphorylated 23-residue peptide was found to be susceptible to mass spectral analysis. Information from the negative ion spectrum was used in conjunction with complete sequence information and experiments which showed that all phosphates were attached to serine residues. Phosphorylated and unphosphorylated serine residues were identified and the sample was shown to be homogeneously octaphosphorylated.

Amino Acid Sequence↗
PubMed1985

Biotin-binding proteins and biotin transport to oocytes.

The eggs of chickens and other birds contain two proteins that bind biotin. Both are homotetrameric proteins of similar size. In contrast to the well-characterized egg white avidin, egg yolk biotin-binding protein has a very acidic isoelectric point, binds biotin with lower affinity, and is usually saturated with biotin. Like other egg yolk proteins, biotin-binding protein appears to be synthesized in the liver, transported by the blood stream to the ovary and deposited in the developing oocyte. Since the yolk of a chicken egg contains over 90% of the biotin in an egg and all of the biotin is bound to biotin-binding protein, the function of biotin-binding protein is undoubtedly to transport biotin to the egg for future use by the developing embryo. Avidin is produced by the oviduct and in the egg it is presumed to deter microbial growth around the oocyte by sequestering biotin. Among the eggs examined, those from turkeys have the lowest amount of biotin-binding protein and the highest amount of avidin. Furthermore, the majority of the biotin in turkey eggs can be bound to avidin in the egg white, suggesting a nutritional role for avidin in turkeys. An assay has been developed to conveniently measure apo- and holobiotin-binding proteins.

Animals↗
PubMed1984

Characterization of virtual coupling in the proton nuclear magnetic resonance spectrum of N,N'-diacetylchitobiose by two-dimensional J-resolved spectroscopy.

The anomeric proton of the reducing N-acetylglucosamine residue of beta-N,N'-diacetylchitobiose exhibited an unusual lineshape indicative of virtual coupling in the 250 MHz proton NMR spectrum. The two-dimensional J-resolved spectrum contained four lines associated with this proton, and this pattern can be used to distinguish virtual coupling from other effects. Anomeric protons of previously studied asparagine-linked glycopeptides which exhibited unusual lineshapes in the conventional NMR spectra did not exhibit the four line patterns indicative of virtual coupling in the two-dimensional J-resolved spectra. Although virtual coupling may partially account for the unusual lineshapes observed in the normal proton NMR spectra, the anomalous behavior observed in the two-dimensional J-resolved spectra of these glycopeptides cannot be explained solely by this phenomenon.

Disaccharides↗
PubMed1984

Highly phosphorylated region of chicken riboflavin-binding protein: chemical characterization and 31P NMR studies.

Phosphate residues on chicken riboflavin-binding protein (RBP) have been implicated in the recognition and deposition of the protein-vitamin complex in egg yolk by the ovary. We demonstrate that all of the phosphate of RBP is linked to serine and that most if not all of the phosphoserine residues are contained in a single tryptic peptide having a composition SerP8, Glx6, His2, Leu2, Ala, Met, Lys. Despite differences in the tissue of synthesis, RBPs isolated from egg yolk and egg white yield phosphopeptides virtually identical in their amino acid composition and 101-MHz 31P NMR spectra. This implies that posttranslational phosphorylation of RBP is the same in liver and oviduct. The 31P NMR spectrum of the phosphopeptide is quite different from that of the phosphoprotein. The 31P NMR spectra of egg yolk and egg white RBP are quite similar but not identical and are unaffected by the binding of riboflavin. Optimal resolution of seven phosphorus resonances was obtained near pH 7.0. The titration behavior of all the phosphoserine residues is similar. We propose that this highly anionic peptide, exposed at the surface of RBP, is the principal determinant for the uptake of RBP by the vitelline membrane of the ovarian follicle.

Amino Acids↗
PubMed1982

Dephosphorylation of chicken riboflavin-binding protein and phosvitin decreases their uptake by oocytes.

Riboflavin-binding protein (RBP) and phosvitin are phosphoglycoproteins transferred from the plasma of laying hens into the yolk of developing oocytes. We have examined the effect of phosphate removal on this yolk deposition process. Unmodified yolk RBP and phosvitin contain, respectively, 8.3 and 109 residues of phosphate/molecule. Complete dephosphorylation of yolk RBP caused a 20-min decrease in the plasma clearance half-life an 87% decrease in the uptake of the protein into oocytes in vivo. Although partially desialylated, dephospho-yolk RBP was identical with the native protein by several criteria, including riboflavin-binding capacity, mobility on SDS-polyacrylamide gels, and circular dichroism. A series of partially dephosphorylated yolk RBP samples, prepared by limited enzymatic hydrolysis, was indistinguishable from native yolk RBP by all criteria except phosphate content. Removal of the 1st phosphate residue decreased uptake of yolk RBP into oocytes by about 60%. Uptake into oocytes could not be restored to dephospho-yolk RBP by addition of anionic groups by succinylation. However, succinylation of native yolk RBP decreased its deposition into oocytes to the same extent as dephosphorylation. Partial dephosphorylation of phosvitin also had marked effects. The plasma clearance of dephosphophosvitin (70% of phosphate removed) was much faster than native phosvitin. After 4 h, 15% of injected 125I-phosvitin remained in circulation compared with only 3.8% of 125I-dephosphophosvitin. The uptake of dephosphovosvitin into oocytes was 79% less than that of native phosvitin. In vitro, 125I-phosvitin bound specifically to a preparation of oocyte plasma membranes as indicated by competition with unlabeled phosvitin but not with RBP. The specific binding of dephosphophosvitin was 96% less than that of native phosvitin and it could be displaced equally well by phosvitin or yolk RBP.

Acid Phosphatase↗
PubMed1982

Carbohydrate compositional effects on tissue distribution of chicken riboflavin-binding protein.

Riboflavin-binding proteins (RBP) purified from chicken egg white, yolk and the serum of laying hens differ in their carbohydrate compositions reflecting tissue-specific modifications of a single gene product. All three are complex glycoproteins having more than twice as many N-acetylglucosamine residues (greater than 12) as mannose residues (approx. 6). Egg white RBP is distinctive in having only one sialic acid and two galactose residues. Serum RBP contains approx. five sialic acid and seven galactose residues. In addition there is one residue of fucose. The carbohydrate composition of yolk RBP indicated the hydrolysis, respectively, of one, one, two and 3 residues of sialic acid, fucose, galactose, and N-acetylglucosamine from its precursor, serum RBP. The effect of these differing levels of glycosylation on plasma clearance, ovarian uptake and tissue distribution of 125I-labeled riboflavin-binding proteins in laying hens were compared. 2 h after intravenous injection, 19% of the egg white RBP, 29% of the yolk RBP, and 37% of the serum RBP remained in circulation. The kinetics of plasma clearance was distinctly biphasic for each of the radioiodinated proteins. The initial rapid-turnover component (t1/2 = 13 min) ranged from 27% of the serum RBP sample to 48% of the egg white RBP sample. The remaining slow-turnover components were cleared with half-lives of 81 min (egg white RBP), 101 min (yolk RBP), and 121 min (serum RBP). 16 h after injection, only 4% of the egg white RBP was deposited in the yolk of developing oocytes while about 12% of the serum RBP and yolk RBP was deposited. This highly significant difference is apparently due to preferential, carbohydrate-dependent clearance of egg white RBP by the liver rather than preferential uptake of serum and yolk RBP by the ovarian follicle. We find no evidence for carbohydrate-directed uptake of riboflavin-binding protein by the ovarian follicle.

Animals↗
PubMed1981

Thiamin deposition in eggs is not dependent on riboflavin-binding protein.

The thiamin content of eggs laid by hens possessing no, one or two functional genes for riboflavin-binding protein is unaffected by the genotype. This does not support the hypothesis of Muniyappa & Adiga [Biochem. J. (1979) 177, 887-894] that the deposition of thiamin-binding protein is coupled to the deposition of riboflavin-binding protein.

Animals↗
PubMed1978

Relationship between biotin-binding proteins from chicken plasma and egg yolk.

The plasma of laying hens contains a specific biotin-binding protein that appears to be identical with an egg-yolk biotin-binding protein. Both proteins are saturated with biotin and require elevated temperatures to effect the exchange of [14C]biotin for the protein-bound vitamin. The heat-exchange curve in each case is the same and differs sharply from that of avidin, the egg-white biotin-binding protein. On Sephadex G-100 gel filtration, plasma and yolk biotin-binding proteins were each eluted slightly ahead of avidin (mol.wt. 68,000), suggesting that they are of similar molecular weight. Plasma and yolk biotin-binding proteins required the same ionic strength to be eluted from a phosphocellulose ion-exchange column. Both the plasma and yolk biotin-binding proteins had a pI of 5; avidin has a pI of 10. Plasma biotin-binding protein cross-reacted with antiserum to yolk biotin-binding protein and showed a precipitin line of identity with purified yolk biotin-binding protein. It is suggested that biotin-binding plays an important role in mediating the transport of the vitamin from the bloodstream to the developing oocyte.

Animals↗