PubMed Health⌕ Search

Biomedical subjects

H B White

Publications and source records attributed to H B White.

At least 19 recordsLinked to original sources
PubMed1992

Separation and characterization of the two Asn-linked glycosylation sites of chicken serum riboflavin-binding protein. Glycosylation differences despite similarity of primary structure.

Serum riboflavin-binding protein, a phosphoglycoprotein from the blood of laying hens, contains two Asn-Xaa-(Thr)Ser sequons in very similar but well-separated regions of amino acid sequence. In order to evaluate the effect of local amino acid sequence on the structure of the attached oligosaccharides, serum riboflavin-binding protein was purified to homogeneity, reduced and alkylated, digested with trypsin, and the two glycopeptides were separated by reversed-phase chromatography. After digestion with peptide-N-glycosidase F the released oligosaccharides were separated by high-pH anion-exchange chromatography and the oligosaccharide profiles of the two glycopeptides were compared. Although the two asparagine residues that are glycosylated are contained in pentapeptide segments in which four out of five amino acids are identical, the array of oligosaccharides present at each site show differences in both type and distribution. This suggests that local secondary or tertiary structure, or the order of glycosylation, influences the oligosaccharide structure more than does the primary structure flanking the attachment site.

Amino Acid Sequence↗
PubMed1992

Effect of riboflavin-binding protein deficiency on riboflavin metabolism in the laying hen.

Normal chicken eggs contain substantial amounts of riboflavin, all of which is bound to a specific, high-affinity, riboflavin-binding protein (RfBP). Two hens, genetically unable to produce RfBP and thus unable to deposit sufficient riboflavin in their eggs, were compared to two normal hens with respect to the biological half-life of [14C]riboflavin, the tissue distribution of 14C-labeled flavins, and the relative contributions of tissue and dietary riboflavin to flavins deposited in the egg. The biological half-life of [14C]riboflavin was slightly but insignificantly less in the RfBP-deficient hens (11.5 +/- 1.7 days vs 15.1 +/- 3.3 days). The 14C-labeled flavin content of a variety of tissues 3 weeks after the intraperitoneal injection of 5 microCi of riboflavin was also very similar among the four hens. In contrast, the 14C-labeled flavin content of egg yolk, egg albumen, and blood plasma from RfBP-deficient birds was less than 10% of normal. For all hens, the specific radioactivity of flavins in yolk and albumen was similar to that in liver but less than that in heart. We conclude that riboflavin deposited in egg had equilibrated with the large hepatic flavin pool and was not derived preferentially from unlabeled dietary riboflavin. Other than the inability to deposit riboflavin in their eggs, hens of the mutant strain have normal riboflavin metabolism.

Administration, Oral↗
PubMed1992

Availability of avidin-bound biotin to the chicken embryo.

Avidin, an exceptionally stable protein in egg white, binds the vitamin biotin with very high affinity and can induce biotin deficiency when fed to animals. To determine if biotin bound to avidin is available to the chicken embryo, the fate of [3H]biotin complexed to avidin was monitored during embryonic development. The majority (greater than 85%) of the [3H]biotin was extraembryonic until the day before hatching, when embryos swallow egg white and withdraw the yolk sac into their abdomen. Thus, biotin in the egg white of chicken eggs contributes little to the biotin status of the chick prior to hatching. After hatching, much of the [3H]biotin was assimilated. About 30% of the total was found in the liver and kidneys by 4 days of age. The biotin in liver was associated with large proteins and not with avidin. In a separate experiment, biotin injected into the egg white of biotin-deficient eggs failed to increase embryonic development or hatchability. Both experiments suggest that biotin in egg yolk is the primary and virtually sole source of biotin for the chicken embryo.

Age Factors↗
PubMed1991

Competitive binding assays for high-affinity binders in the presence of endogenous ligands: application to biotin-binding proteins.

Endogenous ligands complicate radioligand-binding assays of high-affinity binding proteins by obscuring binding sites or by diluting the labeled ligand. We have developed a mathematical model for such systems where radioligand and endogenous ligand are structurally identical. Data which relate radioligand binding at equilibrium as a function of sample volume can be plotted such that the concentrations of endogenous ligand and binder are graphically determined; however, a more precise determination may be done by nonlinear regression with the aid of a microcomputer. The method is demonstrated for the assay of biotin-binding proteins in the presence of a range of endogenous biotin concentrations below and above that required to saturate the binding sites.

Animals↗
PubMed1991

Biotin diffusion in stored chicken eggs: a re-assessment.

1. The possibility that biotin in stored eggs migrates from the yolk into the albumen was re-investigated. 2. Sets of eggs collected from 12 Single Comb White Leghorn hens were stored at 5, 8, 12, 15, or 18 degrees C for 5, 10, 15, 20, or 25 days and then frozen. 3. For each set, yolk and albumen samples adjacent to the yolk membrane were each pooled and assayed for protein-bound biotin by radioligand exchange with non-linear regression analysis of the data. 4. In contrast to previous work reported by Bush and White (Comp. Biochem. Physiol. 93B, 543-547, 1989), no evidence of biotin diffusion was found. 5. Non-linear regression was used to re-evaluate the data from the earlier study, confirming the results, although less strikingly. 6. The discrepancy is partly due to the method of data analysis, although differences in breed or number of hens may also be contributing factors.

Animals↗
PubMed1989

Conversion of domains into subunits in the processing of egg yolk biotin-binding protein I.

Biotin-binding protein I (BBP-I), a protein that differs in its heat stability at low concentrations from that of BBP-II, has been purified from the yolk of hen oocytes and compared to BBP-II. Rabbit antiserum to BBP-II cross-reacts with identity to BBP-I. The molecular mass of BBP-I under denaturing conditions is about 68 kDa, a value four times that of BBP-II. Limited trypsin proteolysis of BBP-I generates subunits of 18 kDa with intermediate forms of approximately 51 and 34 kDa. The NH2-terminal sequence of BBP-I is very similar to that of BBP-II but has little of the polymorphism that is presumed to be generated at several positions by the slightly different subunits of BBP-II. These results indicate an unusual processing pathway in which four tandemly repeated biotin-binding domains of BBP-I become the subunits of BBP-II after limited proteolysis.

Amino Acid Sequence↗
PubMed1989

Avidin traps biotin diffusing out of chicken egg yolk.

1. The unequal distribution of biotin and biotin-binding proteins between the yolk and albumen of freshly laid chicken eggs provides the potential for time-dependent redistribution of biotin that could affect egg quality, biotin availability, and hatchability. 2. Avidin-bound biotin was measured in albumen next to the shell and next to the yolk in eggs stored up to 23 days. 3. Biotin bound to biotin-binding proteins (BBP-I and BBP-II) was measured at the center and periphery of yolk from the same eggs. 4. After 11 days of storage, significant amounts of biotin from the yolk began to accumulate in the albumen adjacent to the yolk. 5. This transfer is attributed to a change in the vitelline membrane that permits diffusion of biotin, not BBP-I or BBP-II, out of the yolk. 6. The dynamics of this phenomenon suggest that in addition to its antimicrobial role, avidin may be involved in the utilization of biotin by the chick embryo.

Animals↗
PubMed1988

Purification and characterization of biotin-binding protein II from chicken oocytes.

BBP-II, the major biotin-binding protein from chicken oocytes, was purified 12,000-fold with a 22% yield. The purification procedure includes butan-1-ol extraction of yolk lipids, phosphocellulose chromatography of the water-soluble proteins, DEAE-cellulose chromatography at pH 7.4 and hydroxyapatite column chromatography. Final purification was obtained by using a second DEAE-cellulose column chromatography at pH 6.0. BBP-I activity separated from BBP-II activity during elution from the first DEAE-cellulose column. Purified BBP-II was homogeneous on both polyacrylamide-gel electrophoresis and SDS/polyacrylamide-gel electrophoresis under conditions that would detect a 1% impurity. The subunit Mr determined from SDS/polyacrylamide-gel electrophoresis was 18,200 (72,600 for tetramer), which compares favourably with an Mr value of 17,300 (69,100) calculated from the amino acid analysis. A single precipitin line formed when rabbit antiserum to the protein was directed against a crude chicken egg-yolk sample. BBP-II purified by this procedure lacked carbohydrate and phosphate, was stable indefinitely when frozen, and was quite stable at room temperature. The N-terminal amino acid sequence showed polymorphism at three positions in the first 23 residues and was about 45% identical with the N-terminal 22 residues of avidin. Antiserum to BBP-II cross-reacted with BBP-I and similar proteins in the yolk of eggs from various birds and alligator as judged by immunodiffusion and enzyme-linked immunosorbent assays. No cross-reaction was observed with chicken egg-white by either of these methods.

Amino Acid Sequence↗
PubMed1988

Chicken riboflavin-binding protein. cDNA sequence and homology with milk folate-binding protein.

The Rd gene is expressed in the livers and oviducts of laying hens and codes for the riboflavin-binding protein (RfBP) of egg yolk and egg white. A lambda gt11 cDNA library derived from chicken oviduct poly(A)+ RNA was screened with polyclonal rabbit antiserum to chicken RfBP. Positive clones were isolated and rescreened with a mixed oligonucleotide probe corresponding to residues 20-25 of the mature protein. The largest cDNA clone (969 base pairs) was subcloned into plasmid pIBI21, and the nucleotide sequence was determined by the dideoxynucleotide method. This clone contained the entire coding region for RfBP. The published amino acid sequence of the mature protein was confirmed. In addition, the following 17-residue signal peptide was deduced: Met-Leu-Arg-Phe-Ala-Ile-Thr-Leu-Phe-Ala-Val-Ile-Thr-Ser-Ser-Thr-Cys. Unexpectedly, the nucleotide sequence codes for 2 adjacent arginine residues at the carboxyl terminus that are not observed in the mature protein. The amino acid sequence of RfBP is homologous with bovine milk folate-binding protein. Eight of the nine pairs of cysteines involved in disulfide bonds in RfBP are conserved in folate-binding protein, as are all of the tryptophan residues. Sequence identity between homologous regions of these two vitamin-binding proteins is more than 30%.

Amino Acid Sequence↗
PubMed1988

Riboflavin-binding protein from reptiles: a comparison with avian riboflavin-binding proteins.

1. Riboflavin-binding protein (RBP) has been isolated for the first time from reptilian sources. 2. RBP from eggs of Python molurus (Indian python) and Chrysemys picta (painted turtle) has been isolated and compared to RBP from Gallus gallus domesticus (chicken), a well-characterized protein, and a newly isolated RBP from Cairina moschata (Muscovy duck). 3. Each of the proteins is phosphorylated and glycosylated. 4. The ratio of riboflavin binding to protein is 1:1 and the KD for each protein is between 1-3 nM. 5. The mol. wts, different for each species, range from 30,000-40,000, with the reptilian proteins being approx. 10,000 larger than the avian proteins.

Amino Acids↗
PubMed1987

Phosphorylation heterogeneity of tryptic phosphopeptides of chicken riboflavin-binding protein.

The tryptic phosphopeptide of hen egg white riboflavin-binding protein has been found to exist as a mixture of peptides which differ only with respect to the number of covalently bound phosphoryl groups. Anion-exchange chromatography was used to separate homologues of the tryptic phosphopeptide of egg white riboflavin-binding protein. Four peptide peaks were obtained and analyzed using plasma desorption mass spectrometry. Molecular ions obtained agree closely with calculated molecular weight values for phosphopeptides with 8, 7 and 5 phosphoryl groups. Amino acid analyses showed that the octa- and hepta-phosphorylated peptides were pure and had the same amino acid compositions.

Animals↗
PubMed1987

Role of avidin and other biotin-binding proteins in the deposition and distribution of biotin in chicken eggs. Discovery of a new biotin-binding protein.

In addition to the previously characterized egg-yolk biotin-binding protein (BBP-I), we have discovered another BBP (BBP-II) in the plasma and yolk from laying hens. BBP-I is stable to 65 degrees C, whereas BBP-II is stable to 45 degrees C. Both proteins are normally saturated with biotin and together they account for most, if not all, of the biotin in hen plasma and yolk, except in hens fed excessive amounts of biotin (greater than 1 mg of biotin/kg of feed). The maximal production of BBP-I is attained at lower levels of dietary biotin (approximately 50 micrograms/kg) than for BBP-II (approximately 250 micrograms/kg); however, the maximal production of BBP-II is severalfold greater than for BBP-I. Consequently, as dietary biotin increases, the ratio of BBP-II to BBP-I increases and becomes constant at dietary intakes of biotin above 250 micrograms/kg. The observation that the amounts of these proteins are limited by biotin in the normal dietary range (less than 250 micrograms/kg) suggests that biotin is required for the synthesis, secretion or stability of these proteins. Although both plasma vitamin-protein complexes are transported to the oocyte and concentrated in the yolk, BBP-II is transferred more efficiently. Thus biotin deposition in the yolk is a function of the amounts and relative concentrations of the two proteins. Dietary biotin above 250 micrograms/kg exceeds the transport capacity of BBP-I and BBP-II in the plasma; however, unbound biotin does not accumulate. Rather it is efficiently scavenged by avidin in the oviduct and transferred to the egg albumen. Only when avidin becomes saturated at high dietary intake does free or weakly bound biotin accumulate in plasma and yolk. The synthesis of avidin is independent of dietary biotin. Small amounts of BBPs with the heat-stability of avidin or BBP-I respectively are present in the plasma of adult males or immature chickens. BBP-II, the major BBP in the plasma and yolk of laying hens, was not detected in the plasma of non-laying chickens.

Animals↗
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↗