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T T Yip

Publications and source records attributed to T T Yip.

At least 37 records · Page 2Linked to original sources
PubMed1994

Detection of Epstein-Barr viral RNA in malignant lymphomas of the upper aerodigestive tract.

Recent studies have suggested a probable etiologic association between Epstein-Barr virus (EBV) and nasal lymphomas, irrespective of geographic location. This study was performed to investigate the strength of association of EBV with non-Hodgkin's lymphomas of the upper aerodigestive tract, based on a large series of cases that have been thoroughly immunophenotyped on frozen tissues. A sensitive in situ hybridization technique was used to detect EBV encoded RNA (EBER) in paraffin sections. Among 30 cases of nasal/nasopharyngeal T-cell lymphoma, 25 (83.3%) were EBER-positive. In the positive cases, most of the neoplastic cells showed strong nuclear signals. Further analysis of this group of tumors showed that all 21 cases (100%) with a CD56+ CD3-phenotype were EBER positive, whereas four of nine cases (44.4%) with a CD56-negative immunophenotype were positive. Only one of 10 cases (10%) of nasal/nasopharyngeal B-cell lymphoma was EBER positive; the positive case was a diffuse mixed-cell lymphoma and could not be distinguished morphologically from the negative cases. Among the 21 cases of lymphoma of the tonsils and back of the tongue (20 B-lineage and one T-lineage), none was EBER positive. In the normal mucosa of the nose/nasopharynx or tonsil (20 cases studied), only very rare EBER-positive small lymphocytes were found in two cases. The almost exclusive detection of EBER in nasal/nasopharyngeal T-cell neoplasms among the lymphomas of the upper aerodigestive tract suggests that EBV probably plays an etiologic role in the pathogenesis of this group of tumors and is not simply a passenger virus, and neither is this merely a site-dependent phenomenon in view of the weak association with nasal/nasopharyngeal B-cell lymphoma.

Herpesvirus 4, Human↗
PubMed1994

Lactoferrin-receptor interaction. Effect of surface exposed histidine residues.

Specific receptors for lactoferrin (Lf) have been identified in the small intestine brush-border membrane and on lymphocytes. Little is known about the mechanism of Lf interaction with its receptor protein. Because of the pH dependence of this interaction, the possible involvement of surface exposed histidine residues was explored. His residues on purified human milk Lf were progressively modified by carboxyethylation with diethyl pyrocarbonate; the reaction was monitored by UV absorbance and by affinity chromatography on immobilized Cu(II) ions. Human infant brush-border membrane vesicles (BBMVs) were prepared by differential centrifugation and precipitation methods. Human peripheral lymphocytes were prepared by Ficoll centrifugation and stimulated by mitogen (PHA) exposure in culture. A competitive receptor binding assay was performed with 59Fe- and/or 125I-labelled native Lf and His-modified Lf. Binding assays with labelled native Lf were conducted in the presence of a 10-200 fold molar excess of DEPC-Lf, the DEPC-Lf was not competitive. A 100-fold molar excess of native Lf completely blocked the interaction of labelled Lf with the receptor. Similar results were obtained for receptor proteins on BBMVs and lymphocytes. Thus, Lf receptors on these two different cell types appear to require His residues for Lf binding.

Adult↗
PubMed1994

Specific association of Epstein-Barr virus with lymphoepithelial carcinoma among tumors and tumorlike lesions of the salivary gland.

The Epstein-Barr virus (EBV)-encoded RNAs in situ localization procedure is a convenient, highly sensitive, and highly specific technique that is applicable to routinely fixed, paraffin-embedded tissue sections; this technique can be used for the study of the association and, hence, the possible causal role of EBV in tumors. This study was performed to elucidate whether EBV plays a role in the pathogenesis of tumors that arise in the salivary glands, since the salivary gland is known to be a reservoir for EBV replication. Cases that were selected included 61 examples of various benign and malignant neoplasms, as well as tumorlike conditions of the major and minor salivary glands. Only the five cases of lymphoepithelial carcinoma (so-called malignant lymphoepithelial lesion) and the single case of metastatic nasopharyngeal undifferentiated carcinoma showed staining with EBV-encoded RNAs, whereas negative findings were found in all of the other cases. In the cases with positive results, all of the neoplastic epithelial cells showed strong nuclear signals, but the lymphoid cells were negative. The consistent association of EBV with lymphoepithelial carcinoma of the salivary gland suggests that the virus probably plays a causal role in this tumor, at least in the Asian population, whereas there is no evidence for a causal role of EBV in other primary tumors of the salivary gland.

Adult↗
PubMed1993

Characterization of the antibody response to the latent infection terminal proteins of Epstein-Barr virus in patients with nasopharyngeal carcinoma.

Human sera were tested for antibodies against the Epstein-Barr virus (EBV) latent infection terminal proteins (TPs). Anti-TP IgG and IgA antibodies were detected by an indirect immunofluorescence assay of insect cells expressing a recombinant TP1. Out of 301 human sera of patients with EBV-related and EBV-unrelated disorders, only sera from patients with nasopharyngeal carcinoma (NPC) (32/83; 38%) showed anti-TP antibodies. Studies on serial sera from German and Hong Kong NPC patients revealed a decline of anti-TP antibodies during tumour therapy, and none of these antibodies were identified in patients with early tumour stages or in remission. Comparative studies of TP1-specific polyclonal rabbit antisera and human TP-positive sera showed clear differences in the TP epitopes recognized by each. Human antisera contained antibodies only to native epitopes in exons 2 to 7 of TP1 whereas rabbit antisera reacted only with epitopes located in the first exon and, additionally, exhibited EBV strain specificities.

Animals↗
PubMed1992

Occupancy of a C2-C2 type 'zinc-finger' protein domain by copper. Direct observation by electrospray ionization mass spectrometry.

The metal ion specificity of most 'zinc-finger' metal binding domains is unknown. The human estrogen receptor protein contains two different C2-C2 type 'zinc-finger' sequences within its DNA-binding domain (ERDBD). Copper inhibits the function of this protein by mechanisms which remain unclear. We have used electrospray ionization mass spectrometry to evaluate directly the 71-residue ERDBD (K180-M250) in the absence and presence of Cu(II) ions. The ERDBD showed a high affinity for Cu and was completely occupied with 4 Cu bound; each Cu ion was evidently bound to only two ligand residues (net loss of only 2 Da per bound Cu). The Cu binding stoichiometry was confirmed by atomic absorption. These results (i) provide the first direct physical evidence for the ability of the estrogen receptor DNA-binding domain to bind Cu and (ii) document a twofold difference in the Zn- and Cu-binding capacity. Differences in the ERDBD domain structure with bound Zn and Cu are predicted. Given the relative intracellular contents of Zn and Cu, our findings demonstrate the need to investigate further the Cu occupancy of this and other zinc-finger domains both in vitro and in vivo.

Copper↗
PubMed1992

Mapping and sequence-specific identification of phosphopeptides in unfractionated protein digest mixtures by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

We have demonstrated a procedure for the rapid (minutes), sensitive (less than pmol), and sequence-specific identification of phosphopeptides in unfractionated digests of phosphoproteins using matrix-assisted UV laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry. The mass-dependent identification of one specific 13-residue phosphopeptide (S105-K117), observed among the 153 possible trypsin digest fragments of human beta-casein (211 residues), was confirmed by amino acid sequence analysis of the 33P-labeled peptide after isolation by reverse-phase HPLC. MALDI-TOF was also used to monitor the rate and extent to which an 18-residue N-terminal beta-casein peptide (R1-K18) was phosphorylated in vitro. These results demonstrate that MALDI-TOF may be used (i) to facilitate the identification of sequence-specific sites of protein phosphorylation and dephosphorylation, (ii) to monitor protein and peptide phosphorylation and dephosphorylation reaction rates, even in complex unfractionated mixtures, (iii) to determine the minimum primary structure necessary for the phosphorylation of specific protein surface domains, and (iv) to evaluate the effects of intact protein phosphorylation and dephosphorylation on susceptibility to subsequent proteolytic events.

Amino Acid Sequence↗
PubMed1992

Synthetic metal-binding protein surface domains for metal ion-dependent interaction chromatography. I. Analysis of bound metal ions by matrix-assisted UV laser desorption time-of-flight mass spectrometry.

To extend the analytical capabilities of immobilized metal ion affinity chromatography (IMAC) for evaluation of biologically relevant peptide-metal ion interactions, we have prepared synthetic peptides representing metal-binding protein surface domains from the human plasma metal transport protein known as histidine-rich glycoprotein (HRG). Three synthetic peptides, representing multiples of a 5-residue repeat sequence (Gly-His-His-Pro-His) from within the histidine- and proline-rich region of the C-terminal domain were prepared. Prior to immobilization, the synthetic peptides were evaluated for identity and sample homogeneity by matrix-assisted UV laser desorption time-of-flight mass spectrometry (LDTOF-MS), a method developed recently for the mass determination of high-molecular-mass biopolymers. 2,5-Dihydroxybenzoic acid was evaluated as a matrix to facilitate the laser desorption and ionization of intact peptides and was found to be ideally suited for determinations of mass within the low-mass region of interest (641.7 to 1772.8 dalton). We observed minimal chemical noise from photochemically generated peptide-matrix adduct signals, clustering, and multiply-charged peptide species. Peptides with bound sodium and potassium ions were observed; however, these signal intensities were reduced by immersion of the sample probe tip in water. Mixtures of the three different synthetic peptides were also evaluated by LDTOF-MS after their elution through a special immobilized peptide-metal ion column designed to investigate metal ion transfer. We found LDTOF-MS to be a useful new method to verify the presence of peptide-bound metal ions.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1992

Synthetic metal-binding protein surface domains for metal ion-dependent interaction chromatography. II. Immobilization of synthetic metal-binding peptides from metal ion transport proteins as model bioactive protein surface domains.

This preliminary investigation tests the premise that biologically relevant (1) peptide-metal ion interactions, and (2) metal ion-dependent macromolecular recognition events (e.g., peptide-peptide interactions) may be modeled by biomimetic affinity chromatography. Divinylsulfone-activated agarose (6%) was used to immobilize three different synthetic peptides representing metal-binding protein surface domains from the human plasma metal transport protein histidine-rich glycoprotein (HRG). The synthetic peptides represented 1-3 multiple repeat units of the 5-residue sequence (Gly-His-His-Pro-His) found in the C-terminal of HRG. By frontal analyses, immobilized HRG peptides of the type (GHHPH)nG, where n = 1-3, were each found to have a similar binding capacity for both Cu(II) ions and Zn(II) ions (31-38 mumol/ml gel). The metal ion-dependent interaction of a variety of model peptides with each of the immobilized HRG peptide affinity columns demonstrated differences in selectivity despite the similar internal sequence homology and metal ion binding capacity. The immobilized 11-residue HRG peptide was loaded with Cu(II) ions and used to demonstrate selective adsorption and isolation of proteins from human plasma. These results suggest that immobilized metal-binding peptides selected from known solvent-exposed protein surface metal-binding domains may be useful model systems to evaluate the specificity of biologically relevant metal ion-dependent interaction and transfer events in vitro.

Amino Acid Sequence↗
PubMed1992

Recognition of transition metal ions by peptides. Identification of specific metal-binding peptides in proteolytic digest maps by UV laser desorption time-of-flight mass spectrometry.

Metal-binding peptides in proteolytic digest maps have been identified by matrix-assisted UV laser desorption time-of-flight mass spectrometry (LDTOF-MS). The plasma and milk metal transport protein chosen to demonstrate this process, histidine-rich glycoprotein (HRG), was purified and then digested with trypsin; the cleavage products were analyzed by LDTOF-MS with dihydroxybenzoic acid as the matrix. The selective interaction of specific peptides with one or more Cu atoms was observed when Cu(II) ions were added to the digest mixture. At least one specific metal-binding peptide was identified by computerized sequence analysis using the molecular mass data and available cDNA sequence. These results demonstrate the first direct observation by mass spectrometry of differential peptide-metal ion interactions in protein digest maps. The ability to evaluate peptide-metal ion interactions, including stoichiometry, with less than 1 pmol of sample improves significantly our ability to identify metal binding domains in metal-binding proteins.

Amino Acid Sequence↗
PubMed1992

Identification of histidine-rich glycoprotein in human colostrum and milk.

Histidine-rich glycoprotein (HRG) is a 74-kD glycoprotein, originally discovered in plasma, which contains an unusually large amount of histidine (13 mol%) and proline (13 mol%). The specific functions of this protein remain unclear, although it binds (reversibly) transition metal ions such as Cu(II) and Zn(II) with high capacity (10-13 equivalent) and moderate to high affinity (kd = 0.2-10 microM). Because the bioavailability of Cu(II) and Zn(II) ions in human milk is high, we have used specific antibodies from polyclonal antisera directed against purified human plasma HRG to investigate whether this or a related protein is a component of human colostrum and(or) mature milk. Fresh human colostrum (d 1-3) and milk (d 4-120) were collected in the presence and absence of multiple protease inhibitors and EDTA. Immuno "dot" blot analyses and ELISA were developed; HRG was present in both colostrum (0.13-10 micrograms/mL) and mature milk (0.1-10 micrograms/mL). Unidentified components in colostrum and milk, however, were found to depress HRG antigenicity in these assays. Western transfer and immunoblots of denatured colostrum and milk samples analyzed by SDS-PAGE revealed the presence of an immunoreactive band at 74-78 kD, with other bands at 47 and 24 kD under both reducing and nonreducing conditions; smaller immunoreactive fragments (12-14 kD) were detected in some samples. We observed at least one additional band of immunoreactivity of greater molecular mass (greater than 110 kD) in colostrum under nonreducing conditions; we did not observe these bands in plasma samples. Immunoaffinity and Zn(II) affinity isolation of HRG from colostrum and milk resulted in the copurification of several associated proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Proteins↗
PubMed1991

Protein interactions with surface-immobilized metal ions: structure-dependent variations in affinity and binding capacity with temperature and urea concentration.

We have used equilibrium binding analyses to evaluate the influence of temperature and urea on the affinity of hen egg white lysozyme and bovine pancreatic ribonuclease A for surface-immobilized Cu(II) ions. Linear Scatchard plots suggested that these model proteins were interacting with immobilized metal ions via a single class of intermediate-affinity (Kd = 10-40 microM) binding sites. Alterations in temperature had little or no effect on the immobilized Cu(II) binding capacity of either protein. Temperature effects on the interaction affinity, however, were protein-dependent and varied considerably. The affinity of lysozyme for immobilized Cu(II) ions was significantly decreased with increased temperature (0 degree C-37 degrees C), yet the affinity of ribonuclease did not vary measurably over the same temperature range. The van 't Hoff plot (1n K vs 1/T) for lysozyme suggests a straight line relationship (single mechanism) with a delta H of approximately -5.5 kcal/mol. Urea effects also varied in a protein-dependent manner. A 10-fold reduction in the affinity of lysozyme for the immobilized Cu(II) was observed with the urea concentrations up to 3 M; yet urea had no effect on the affinity of ribonuclease for the immobilized metal ions. Although the interaction capacity of lysozyme with the immobilized Cu(II) ions was decreased by 50% in 3 M urea, ribonuclease interaction capacity was not diminished in urea. Thus, temperature- and urea-dependent alterations in protein-metal ion interactions were observed for lysozyme but not ribonuclease A. The complete, yet reversible, inhibition of lysozyme- and ribonuclease-metal ion interactions by carboxyethylation with low concentrations of diethylpyrocarbonate provided direct evidence of histidyl involvement. The differential response of these proteins to the effects of temperature and urea was, therefore, interpreted based on calculated solvent-accessibilities and surface distributions of His residues, individual His residue pKa values, and specific features of the protein surface structure in the immediate environment of the surface-exposed histidyl residues. Possible interaction mechanisms involved in protein recognition of macromolecular surface-immobilized metal ions are presented.

Animals↗
PubMed1991

Structurally intact (78-kDa) forms of maternal lactoferrin purified from urine of preterm infants fed human milk: identification of a trypsin-like proteolytic cleavage event in vivo that does not result in fragment dissociation.

Two forms of lactoferrin, an intact lactoferrin and a "nicked" but apparently intact (i.e., 78-kDa) form, have been isolated from the urine of preterm infants fed human milk. These two forms of lactoferrin, demonstrated to be entirely of maternal origin, were copurified using affinity columns of immobilized single-stranded DNA-agarose. The relative concentrations of the intact lactoferrin and the "nicked" lactoferrin were determined after denaturation and separation by reverse-phase HPLC. N-terminal sequence analyses showed that the intact 78-kDa form had lost two residues from its N terminus. The nicked 78-kDa form was composed of only two fragments; one fragment was identified as the N terminus of the N-lobe (residues 3-283). The other fragment started with Ser-284 and included the alpha-helical structures at the C terminus of the N-lobe, as well as the entire C-lobe. Although no disulfide bonds connect these two fragments, they were tightly associated in vivo and were not separated in vitro except under denaturing conditions. Limited in vitro digestion of human milk lactoferrin with trypsin produced a nicked, but stable (78-kDa), form of DNA-binding lactoferrin nearly indistinguishable from the isolated urinary lactoferrin, except for the absence of one additional arginine residue at the N terminus of the N-lobe. Residues involved in the stable molecular interaction between fragments were evaluated using data obtained from the high-resolution crystal structure of hololactoferrin. Two features, entirely within the N-lobe, account for the lack of fragment dissociation after cleavage at residue 283 in vivo: an extensive interface at the hinge region behind the iron-binding cleft and an "anchor" sequence traversing the remainder of the N-lobe at 90 degrees relative to the fragment interface. These results document the remarkably limited degradation of absorbed lactoferrin in vivo and suggest that iron-binding activity, receptor-binding properties, and postulated immune cell regulatory functions remain intact.

Amino Acid Sequence↗
PubMed1991

Metal ligand-induced alterations in the surface structures of lactoferrin and transferrin probed by interaction with immobilized copper(II) ions.

We have evaluated immobilized Cu(II) ions as a potential site-directed molecular probe to monitor ligand-induced alterations in protein surface structures. Metal ion-induced alterations in the surface structures of different lactoferrins (human and porcine), transferrins (human and rabbit), and ovotransferrin (chicken) were examined. Although these 78,000-dalton glycoproteins are related gene products with similar overall structure and function, they differ greatly in the number and distribution of surface-exposed electron-donor groups thought to interact with Cu(II) ions. Each of these proteins interacted with immobilized Cu(II) ions through sites which are distinct from the two specific high affinity metal binding sites identified for iron. In both the presence and absence of bound iron, transferrins interacted more strongly with the immobilized Cu(II) ions than did lactoferrins; ovotransferrin interacted only weakly. Although iron binding increased the affinities of lactoferrins for immobilized Cu(II), iron binding decreased the affinities of transferrins and ovotransferrin for immobilized Cu(II) ions. Iron-saturated and iron-free lactoferrins were resolved by pH gradient elution, but only in the presence of 3 M urea; they were not resolved by imidazole affinity elution. Conversely, the iron-saturated and iron-free forms of transferrin were only separated by imidazole affinity elution. Urea did not influence the resolution of apo and holo ovotransferrins by imidazole. The differential effects of urea and imidazole suggest the participation of different types of surface electron-donor groups. The progressive site-specific modification of surface-exposed histidyl residues by carboxyethylation revealed several lactoferrin forms of intermediate affinity for immobilized iminodiacetate-Cu(II) ions. In summary, independent of species, the affinity for immobilized Cu(II) ions increased as follows: iron-saturated ovotransferrin less than metal-free ovotransferrin less than apolactoferrin less than hololactoferrin much less than diferric or holotransferrin less than monoferric transferrin less than apotransferrin. We have demonstrated the use of immobilized Cu(II) ions to distinguish and to monitor ligand-induced alterations in protein surface structure. The results are discussed in relation to protein surface-exposed areas of electron-donor groups.

Animals↗
PubMed1991

Origin of intact lactoferrin and its DNA-binding fragments found in the urine of human milk-fed preterm infants. Evaluation by stable isotopic enrichment.

The origin of intact (78-kD) lactoferrin found in the urine of human milk-fed preterm infants was investigated using human milk containing proteins enriched with [13C]leucine and [15N2]lysine or [2H4]lysine. Mothers of infants selected for the study were infused i.v. with [13C] leucine and [15N2]lysine or [2H4]lysine to label milk proteins. The labeled milk was collected from each mother, pooled, fortified with a lyophilized human milk fraction, and fed to her preterm infant by continuous orogastric infusion for a period of 48 h. Urine was collected from each infant for 96 h. Intact lactoferrin (78 kD) and DNA-binding lactoferrin fragments (51 and 39 kD) were purified from the urine by affinity chromatography on columns of immobilized single-stranded DNA-agarose. The concentration and isotopic enrichment of the intact lactoferrin and DNA-binding fragments were determined separately after their isolation by high-performance reverse-phase (phenyl) chromatography. Mass spectral analyses indicated that the isotopic enrichment of the purified urinary lactoferrin was 87 to 100% of that in the labeled human milk lactoferrin. Similar results were obtained for the isolated DNA-binding lactoferrin fragments. The ratios of isotopically labeled leucine to lysine in the purified milk lactoferrins and urinary lactoferrins were similar for each mother/infant pair. Isotopically labeled lysine, added to the milk as free amino acid, was not incorporated into the purified urinary lactoferrin. These results demonstrate that undegraded (78-kD) lactoferrin of maternal origin is absorbed by the gut and excreted intact in the urine of preterm infants; nearly all of the urinary lactoferrin was of maternal origin. The possible immunoregulatory functions of the absorbed intact, maternal lactoferrin are discussed.

DNA-Binding Proteins↗
PubMed1990

Protein interactions with immobilized transition metal ions: quantitative evaluations of variations in affinity and binding capacity.

The interaction of proteins with immobilized transition-metal ions proceeds via mechanisms influenced by metal type and degree of coordination, variations in mobile phase constituents, and protein surface architecture at or near the metal binding site(s). The contributions each of these variables make toward the affinity of protein surfaces for immobilized metal ions remain empirical. We have used equilibrium binding analyses to evaluate the influence of pH and competitive binding reagents on the apparent equilibrium dissociation constant (Kd) and binding capacity of immobilized Cu(II) and Ni(II) ions for several model proteins of known three-dimensional structure. Linear Scatchard plots suggested that 8/13 of the proteins evaluated interacted with immobilized metal ions via a single class of operational (Kd = 10-700 microM) binding sites. Those proteins with the highest affinities for the immobilized Cu(II) ions (5/13) showed evidence of multiple, non-identical or nonindependent binding sites. The effects of altered metal type, pH, and concentration of competitive affinity reagents (e.g., imidazole, free metal ions) on the apparent Kd and binding capacity varied in magnitude for individual proteins. The presence of free Cu(II) ions did not detectably alter either the affinity or binding capacity of the proteins for immobilized Cu(II) ions. The expected relationship between the relative chromatographic elution sequence and calculated affinity constants was not entirely evident by evaluation under only one set of conditions. Our results demonstrate the utility of nonchromatographic equilibrium binding analyses for the quantitative evaluation of experimental variables affecting the relative affinity and capacity of immobilized metal ions for proteins. This approach affords the opportunity to improve understanding and to vary the contribution of interaction mechanisms involved.

Adsorption↗
PubMed1990

Secretory IgA, IgG, and IgM immunoglobulins isolated simultaneously from colostral whey by selective thiophilic adsorption.

In order to evaluate the collective contribution of immunoglobulins to gastrointestinal and immune system development in newborn infants, it would be advantageous to develop a simple and rapid procedure for the selective and quantitative removal of all immunoglobulin classes from colostrum and milk. Toward this end, the major immunoglobulin classes typically present in colostrum (IgM, sIgA, and IgG) have been isolated simultaneously by selective removal from a porcine colostral whey model system using a single-step, preparative scale procedure termed thiophilic adsorption. At neutral pH, the salt-promoted thiophilic affinity of immunoglobulins for the synthetic sulfone-thioether ligands exploits a common (as yet unknown) structural feature of immunoglobulins. The adsorption and recovery procedures operate efficiently under mild buffer conditions permitting the subsequent comparative biochemical analyses of individual immunoglobulin classes for structural and functional heterogeneity. Thus, 1 liter columns of thiophilic adsorbent (T-gel) were employed to obtain pure, structurally intact immunoglobulins from 1 liter batches of porcine colostral whey. The identity and purity of the isolated immunoglobulins were determined under both structure-stabilizing ('native') conditions and denaturing conditions using high-performance size-exclusion chromatography, sucrose density gradient centrifugation, immunodiffusion techniques, SDS-polyacrylamide gradient gel electrophoresis with immunoblotting identification procedures, and two-dimensional electrophoresis. This is the first procedure known to us that allows for the simultaneous one-step isolation (under homologous conditions) of various immunoglobulins with preserved quaternary structure and apparent biological activity.

Adsorption↗
PubMed1990

Differential interaction of peptides and protein surface structures with free metal ions and surface-immobilized metal ions.

We have examined the influence of free metal ions on the affinity of structurally-defined proteins and peptides for model surface-immobilized metal ions. The model proteins chosen differed widely in both the type and quantity of surface-accessible electron donor groups. Metal ion affinity chromatography and equilibrium binding analyses demonstrated that the presence of excess free Cu(II) ions did not measurably affect either the affinity or the binding capacity of lysozyme for immobilized iminodiacetate-Cu(II). Similarly, the presence of excess free Cu(II) ions did not detectably affect the chromatographic behavior or measured affinity of either copper-saturated lactoferrin or iron-saturated lactoferrin for the immobilized Cu(II) ions. Its binding capacity however, was diminished. The affinities of small peptides for immobilized Cu(II) ions was found to be related to their number of His residues. Peptides with 0, 1, 2 and 3 His residues were resolved by high-performance immobilized Cu(II) affinity chromatography in both the presence and absence of added Cu(II) ions. In the presence of excess free Cu(II) ions, however, retention (affinities) of these peptides by immobilized Cu(II) ions was increased in relation to their number of His residues. These data demonstrate that protein surface binding sites for free and immobilized metal ions are functionally distinct. The presence of free and/or protein surface-bound metal ions does not preclude interaction with the same immobilized metal ions. Stationary phase immobilized metal ions can be a useful model system through which we can better understand the influence of macromolecular surface-immobilized metal ions on macromolecular recognition events. The significance of these findings are also important to the design of other site-specific and domain-specific affinity reagents involving metal ions.

Apoproteins↗