Comparison of methods for erythroblast selection: application to selecting fetal erythroblasts from maternal blood

BACKGROUND

Many methods have been employed to obtain fetal cells from maternal blood for prenatal diagnostics, but there has been little work done that compares the efficacy of different methods. This study presents a comparison of two commonly used methods for selecting erythroblasts with selection directly from whole blood.

METHODS

Erythroblasts were isolated from maternal blood by either differential lysis or density separation, followed by selection with an antibody to the transferrin receptor. These methods were compared with antibody selection directly from whole blood. The total yield of erythroblasts was determined for each method.

RESULTS

Red cell lysis is not recommended because the lysis step cannot be well controlled. Density separation followed by antibody selection works well. However, a faster and simpler method, antibody selection directly from whole blood using Immunicon Ferrofluid and magnetic separators, works as well and has the potential to yield even more cells.

CONCLUSIONS

Considering the need for a simple and quick method for selecting fetal cells from maternal blood, we suggest selection directly from whole blood.

A novel method for depositing erythroid cells onto glass slides for fetal cell analysis

BACKGROUND

We have developed a method for selecting erythroblasts from blood, the first step toward identifying fetal cells in maternal blood for diagnostic purposes. Because the selection method results in a large number of positive cells, we needed to develop new methods to deposit the cells onto slides and to modify in situ hybridization procedures to enable detection of fetal cells.

METHODS

We utilized Nunc flaskettes to increase the slide surface area available for cell deposition. The ability of erythroid lineage cells to adhere to several surface modifications was examined. In situ hybridization methods were tested to find the best approach that is compatible with these cell preparations.

RESULTS

The best glass slide coating for erythroid cells was found to be an antibody to glycophorin A, a red cell surface antigen. We were able to get excellent in situ hybridization signals in cells on flaskettes by modifying fixation and pretreatment parameters.

CONCLUSIONS

The methods described here appear to be the best way of attaching a large number of erythroid lineage cells to slides and of detecting them by in situ hybridization.

Cell-growth control by monomeric antigen: the cell surface expression of lysozyme-specific Ig V-domains fused to truncated Epo receptor

Previously we have shown that the V(H) and V(L) fragments of an anti-hen egg lysozyme (HEL) antibody HyHEL-10 are weakly associated but can be driven together by antigen. By joining these antibody variable domains to the cytoplasmic portion of the murine erythropoietin receptor, we created a chimeric growth factor receptor that could be activated by HEL. After co-transfection with two plasmids encoding the respective chimeric receptors in IL-3 dependent murine pro-B Ba/F3 cells, a portion of the cells survived under antigen dependent stimulation without IL-3. These surviving cells all showed coexpression of the two chimeric receptor chains and demonstrated HEL dose-dependent growth stimulation without IL-3. When another IL-3 dependent cell line 32D was transfected with a variant of such chimeric receptor with a linker peptide (Gly-Ser-Gly) inserted between V(H)/V(L) and EpoR domains, an improved growth response was attained. These observations suggest the utility of heterodimeric Fv chimeric receptors in creating cells that respond to monomeric antigen.

Fluorolabeling of antibody variable domains with green fluorescent protein variants: application to an energy transfer-based homogeneous immunoassay

A site-specific and efficient fluorolabeling of antibody variable regions with green fluorescent protein (GFP) variants and its application to an energy transfer-based homogeneous fluoroimmunoassay (open sandwich FIA) were attempted. Two chimeric proteins, Trx-V(H)-EBFP and Trx-V(L)-EGFP, consisting of V(H) and V(L) fragments of anti-hen egg lysozyme (HEL) antibody HyHEL-10 and two GFP color variants, EBFP and EGFP, respectively, were designed to be expressed in cytoplasm of trxB - mutant Escherichia coli as fusions with thioredoxin from E.coli The mixture of two proteins could be purified with HEL-affinity chromatography, retaining sufficient intrinsic fluorescence and binding activity to HEL. A significant increase in fluorescence resonance energy transfer (FRET) dependent on HEL concentration was observed, indicating the reassociation of the V(H) and V(L) domains of these chimeric proteins due to co-existing antigen. With this open sandwich FIA, an HEL concentration of 1-100 microg/ml could be non-competitively determined. The assay could be performed in a microplate format and took only a few minutes to obtain a sufficient signal after simple mixing of the chimeric proteins with samples. This represents the first demonstration that the FRET between GFP variants is applicable to homogeneous immunoassay.

Open sandwich ELISA with V(H)-/V(L)-alkaline phosphatase fusion proteins

The Sandwich ELISA is a widely used technique to measure antigen concentration. Recently, a novel ELISA based on the interchain interaction of separated V(H) and V(L) chains from a single antibody variable region (Fv) was proposed (Open Sandwich ELISA). Since it employs a single antibody recognizing one epitope, the assay requires, in essence, only one cycle of incubation and washing steps. To demonstrate this directly, we have constructed a recombinant gene fusion encoding the V(H) chain of an anti-hen egg lysozyme (HEL) antibody HyHEL-10 and Escherichia coli alkaline phosphatase (V(H)-PhoA). The same type of gene fusion using V(L) chain instead of V(H) chain (V(L)-PhoA) was also constructed and the proteins were obtained with an E. coli expression/secretion system. Open Sandwich ELISAs were performed using microtiter plates with immobilized V(L) or V(H) fragment, and V(H)-PhoA or V(L)-PhoA, respectively, as the detection reagent which was simultaneously added to each well with samples. As a result, HEL concentrations in the samples were determined after one round of incubation and washing steps, with a signal generated in a direct relationship to the concentration of HEL added to the reaction mixture. The minimum detectable HEL concentration was approximately 10 ng/ml, which was almost equal to the value previously obtained with plate-immobilized V(L) and V(H) fragment displayed on M13 phage. When the active-site mutant V(H)-PhoA(D101S) was employed instead of V(H)-PhoA and reacted at an optimum pH of 10, a significant enhancement in signal was attained.

Interaction and effect of annealing temperature on primers used in differential display RT-PCR

Differential display of mRNA is a simple, sensitive and powerful method to identify differentially expressed gene fragments. The main drawback of differential display is the lack of reproducibility and the inability to read and compare complex gels. This issue results from employing unoptimized primer combinations and non-specific amplification, most likely due to unavoidable low annealing temperatures. In order to display most of the expressed transcripts (80-120 bands/lane), 26 different 5' primers were used in conjunction with nine different 3' poly (dT) primers. These primer combinations, used with the optimized annealing temperature for each set of primers, produced highly reproducible bands. BSA has a direct effect on the number of bands resolved. Variations in ramping time (9-40 s) had little or no effect on the resolution and reproducibility of differential display.

A high affinity digoxin-binding protein displayed on M13 is functionally identical to the native protein

Phage display of peptides and proteins has successfully been employed to produce binding molecules of altered affinity. Little is known, however, regarding the impact on affinity measurements of phage-displayed molecules compared to their native freely soluble configuration. That identical affinities can be obtained was shown by Scatchard analysis of the native antibody, its single chain derivative (scFv), and its phage-displayed single chain counterpart for the ligand digoxin. No significant difference, within one standard deviation, was detected in affinity for digoxin when the phage-displayed scFv was compared to either its soluble scFv form or the purified antibody. In addition, no change in binding specificity was detected, within two standard deviations, when the binding proteins were challenged with two commonly cross-reactive compounds (dihydrodigoxin and digitoxin). That phage-display can be employed for molecules having high binding affinities (Kd of 6 x 10(-11) M) is also shown.

Effects of islet hormones on amylase secretion and localization of somatostatin binding sites

The interaction of insulin and somatostatin on amylase secretion was examined in the isolated perfused rat pancreas. Exogenous insulin (10 mU/ml) significantly potentiated cholecystokinin- (CCK; 0.5 mU/ml) stimulated amylase secretion (12.47 +/- 2.9 micrograms/ml, n = 7). Glucose (16.7 mM) stimulated endogenous insulin secretion (523 +/- 66 microU/ml) and also significantly enhanced CCK-stimulated amylase secretion (13.41 +/- 2.8 micrograms/ml, n = 11). When somatostatin was included in the perfusion media, containing insulin and CCK, amylase secretion was reduced to 3.17 +/- 0.83 micrograms/ml (n = 7), a level comparable to that of CCK-stimulated amylase secretion alone. Similarly, addition of exogenous somatostatin to perfusion media, containing 16.7 mM glucose and CCK, reduced amylase secretion to 4.29 +/- 1.09 micrograms/ml (n = 9). The effect of somatostatin and insulin on carbamylcholine-stimulated amylase secretion was also examined. Exogenous insulin (50 mU/ml) potentiated carbamylcholine- (10(-8) M) stimulated amylase secretion, and addition of exogenous somatostatin to the media containing both insulin and carbamylcholine suppressed the insulin potentiation. Uptake of 125I-[Tyr11]somatostatin in the perfused pancreas was saturable as it decreased significantly with the addition of excess unlabeled somatostatin. Autoradiograms revealed uptake of the ligand by both the endocrine islets and the exocrine pancreas with the highest density of grains observed over the acini. These results support the hypothesis that islet peptides modulate the exocrine pancreas, that somatostatin inhibits amylase secretion by inhibiting the action of insulin, and that somatostatin may act directly on the exocrine pancreas via specific receptors on acinar cells.

Differential expression of a gene for a methionine-rich storage protein in maize

A methionine-rich 10 kDa zein storage protein from maize was isolated and the sequence of the N-terminal 30 amino acids was determined. Based on the amino acid sequence, two mixed oligonucleotides were synthesized and used to probe a maize endosperm cDNA library. A full-length cDNA clone encoding the 10 kDa zein was isolated by this procedure. The nucleotide sequence of the cDNA clone predicts a polypeptide of 129 amino acids, preceded by a signal peptide of 21 amino acids. The predicted polypeptide is unique in its extremely high content of methionine (22.5%). The maize inbred line BSSS-53, which has increased seed methionine due to overproduction of this protein, was compared to W23, a standard inbred line. Northern blot analysis showed that the relative RNA levels for the 10 kDa zein were enhanced in developing seeds of BSSS-53, providing a molecular basis for the overproduction of the protein. Southern blot analysis indicated that there are one or two 10 kDa zein genes in the maize genome.

Immunolocalization of islet amyloid polypeptide (IAPP) in pancreatic beta cells by means of peroxidase-antiperoxidase (PAP) and protein A-gold techniques

A novel putative polypeptide hormone identified as islet amyloid polypeptide (IAPP) was recently purified from islet amyloid (IA) of diabetic humans and cats, and also from amyloid of a human insulinoma. Although the function of IAPP is yet unknown, its occurrence in pancreatic endocrine tissue and its partial amino acid sequence identity with calcitonin gene-related peptide (CGRP) suggests an endocrine regulatory effect. In the present investigation, the authors utilized antisera to insulin, glucagon, somatostatin, pancreatic polypeptide, synthetic human CGRP, and a synthetic human IAPP (7-17) undecapeptide to immunohistochemically (PAP technique) document the presence of IAPP immunoreactive cells in the islets of the cat, dog, mouse, and rat, but not in the islets of the horse or calf. In serial sections of islets from these species it was shown that IAPP immunoreactivity occurred in insulin-reactive beta cells. This observation was confirmed immunocytochemically in cat islets by means of protein A-gold probes. With protein A-gold labeling techniques, IAPP immunoreactivity was localized to the outer lucent compartment of the beta cell secretory granule, whereas insulin immunoreactivity was associated with the electron-dense core. These findings provide strong evidence that IAPP or an IAPP precursor is synthesized by beta cells and is stored in beta cell granules for subsequent co-secretion with insulin. The conservation of IAPP in humans and multiple animal species and the localization of IAPP to pancreatic beta cells provide further evidence that IAPP has an important endocrine regulatory function. The propensity of IAPP to polymerize and form IA fibrils in diabetes associated with aging may indicate that IAPP is in some way also linked to the development of Type 2 diabetes.

Identification of gastrin molecular variants in gastrinoma syndrome

The molecular species of gastrin in the circulation and in tumor extracts were studied in two groups of patients: (1) with benign gastrinoma and (2) with gastrinoma with liver metastases. Radioimmunoassays (RIAs) and immunoaffinity chromatography for the amino (NH2)- and amidated COOH-terminus of gastrin-17 (antiserum G17) and the NH2-terminus of gastrin-34 (antiserum G34) were employed. In both benign and metastatic tumors the molecular forms of gastrin in boiling water extracts measured by the gastrin-17 NH2- and COOH-terminal assays were similar. In addition to a molecular component resembling the amidated gastrin-17, there were also significant amounts of larger molecular weight (mol. wt.) forms. The larger mol. wt. forms absorbed by the NH2-terminus of G17 antiserum corresponded to the COOH-terminus-extended forms of gastrin-17. Furthermore, larger mol. wt. gastrins immunopurified by antiserum to the NH2-terminus of gastrin-34 corresponded to gastrin-34 extended molecules. Sera of patients with liver metastases had higher concentrations of the NH2-terminal of gastrin-17 whereas sera of patients with benign gastrinoma contained predominantly gastrins detected by the COOH-terminal assay. These results suggest that: (a) there are differences in the molecular pattern of gastrin in the circulation of patients with benign and metastatic gastrinomas; (b) gastrins which are fully processed with carboxy-terminal amidation predominate in the circulation of patients with benign gastrinoma; and (c) gastrins containing the gastrin-17 and COOH-terminally extended gastrin-17 and gastrin-34 precursor molecules occur in high concentration in the circulation of gastrinoma patients with metastases to the liver.

Identification and initial characterization of adipokinetic hormone-like immunoreactive peptides of rat origin

An antiserum was raised to adipokinetic hormone (AKH), a 10-amino-acid-residue peptide found in the arthropod Locusta migratoria. The antiserum demonstrated not only immunocytochemical reaction with some other arthropod species, but also stained many areas of the rat CNS, certain islet cells of the pancreas, and some anterior pituitary cells. The pattern of staining was unlike that for any known rat neuropeptide or hormone. With the antiserum used as the detection system, HPLC and high-voltage electrophoresis yielded two peptides that were purified to homogeneity from rat hypothalamic median eminence. These peptides have unique amino acid compositions, indicating they may be heretofore unknown rat neuropeptides.

Biosynthesis of an asparagine-linked oligosaccharide-containing calcitonin by a rat medullary thyroid carcinoma cell line

Calcitonin contains an amino acid sequence that provides a potential site for glycosylation of the peptide at the asparagine at position 3. Preliminary evidence has suggested that there are glycosylated forms of calcitonin and its precursor, procalcitonin. The CA-77 rat medullary thyroid carcinoma cell line, recently developed to study calcitonin biosynthesis, was used to demonstrate the synthesis of glycosylated forms of this hormone by intact cells. Cultures were incubated in medium containing either [3H]mannose or [35S]methionine. Two species incorporating both labels were specifically immunoprecipitated when cell extracts were treated with calcitonin antibodies. Gel filtration chromatography in 6 M guanidine hydrochloride indicated that one peptide had a molecular weight of 5500, approximately 2000 daltons larger than calcitonin, while the second peptide had a molecular weight of 14 400, the approximate size of procalcitonin. Treatment of the [3H]mannose-labeled cell extract with endo-beta-N-acetylglucosaminidase H before immunoprecipitation removed the labeled sugar from the calcitonin species. Microsequence analysis of the radiolabeled immunoreactive 5500-dalton calcitonin species showed methionine at cycle 8 and mannose at cycle 3, suggesting that this peptide is calcitonin containing an N-linked oligosaccharide at Asn-3. These results suggest that in this cell line a minor but significant biosynthetic pathway exists for the production of glycosylated calcitonin from glycosylated procalcitonin.

Biosynthesis of calcitonin by a rat medullary thyroid carcinoma cell line

The 32-amino acid form of the peptide hormone calcitonin is the product of a series of post-translational processing steps of a 13,400-dalton precursor, procalcitonin. We have now identified the steps involved in proteolytic paring of the precursor to the mature secretory form. Cultures of the CA-77 cell line were radiolabeled and the various forms of calcitonin were isolated by specific immunoprecipitation followed by fractionation on gel filtration and reversed-phase high performance liquid chromatography. Pulse-chase kinetics showed that procalcitonin was cleaved to a 6,500-dalton biosynthetic intermediate which was subsequently processed to the size of mature calcitonin (3,400 daltons). Partial microsequencing of the [35S] methionine-labeled intermediate indicated that the sequence consisted of the COOH-terminal 52 residues of procalcitonin. Partial microsequencing of the [35S]methionine- or [3H]proline-labeled 3,400-dalton species revealed that it was indistinguishable from naturally occurring, amidated calcitonin. These data define the major pathway for calcitonin biosynthesis in this neoplastic cell line and presumably in normal cells.

An amino-terminal tryptophan derivative which is refractory to Edman degradation

A new derivative of tryptophan is proposed to account for the observation that some peptides having amino-terminal tryptophan residues become refractory to Edman degradation. An acid-catalyzed oxidation of the indole nucleus and subsequent cyclization to a unique 3-anilinopyrrolidin-2-one derivative with cleavage of the peptide chain is the most likely chemical explanation. This amino acid is reactive with ninhydrin and contains an aryl amine. However, the amine does not bond to the alpha carbon so while reactive to phenyl isothiocyanate, distances are too great for the residue to be cleaved from the peptide during Edman degradation.

Derivatives of cyclosporin compatible with antibody-based assays: I. The generation of [125I]-labeled cyclosporin

The immunosuppressive drug cyclosporin A, has been successfully iodinated to a specific activity of 300 Ci per gram. 125I-labeled cyclosporin and [3H]cyclosporin are nearly equivalent as tracers in a radioimmunoassay in producing standard lines (suppression by unlabeled cyclosporin) and in assigning values to clinical samples. In addition, the [125I]-labeled cyclosporin has greater than twice the sensitivity, and it is stable to long-term storage. Use of a [125I]-labeled cyclosporin tracer is more convenient, more reproducible, more precise, and easier than the tritiated-cyclosporin alternative in radioimmunoassay of this compound.

Derivatives of cyclosporin compatible with antibody-based assays: I. The generation of [125I]-labeled cyclosporin

The immunosuppressive drug cyclosporin A, has been successfully iodinated to a specific activity of 300 Ci per gram. 125I-labeled cyclosporin and [3H]cyclosporin are nearly equivalent as tracers in a radioimmunoassay in producing standard lines (suppression by unlabeled cyclosporin) and in assigning values to clinical samples. In addition, the [125I]-labeled cyclosporin has greater than twice the sensitivity, and it is stable to long-term storage. Use of a [125I]-labeled cyclosporin tracer is more convenient, more reproducible, more precise, and easier than the tritiated-cyclosporin alternative in radioimmunoassay of this compound.

Amino acid sequence and secondary structural analysis of the corn inhibitor of trypsin and activated Hageman Factor

The amino acid sequence of a corn inhibitor for trypsin and activated Hageman Factor (Factor XIIa) was determined by automated Edman degradation from the intact inhibitor and two fragments generated by specific cleavage of the inhibitor. The 112-residue sequence is unique at each position except 91, where both Ala and Glu were found. The structural heterogeneity suggests the occurrence of two genes (possibly allelic) for the inhibitor. Based on analysis of fragments produced by the interaction of the inhibitor with trypsin-agarose, the reactive site peptide bond is identified as Arg 36-Leu 37. There is no strong similarity between the sequence of the corn inhibitor and the sequences published for other serine protease inhibitors. Thus, the corn inhibitor represents a new family of protease inhibitors. Circular dichroism measurements and a theoretical prediction of secondary structure indicate that the inhibitor has helix and beta sheet contents of approximately 40 and 20%, respectively.

Identification of procalcitonin in a rat medullary thyroid carcinoma cell line

As a first step in studying the biosynthesis of the peptide hormone calcitonin, we have identified procalcitonin species in CA-77 cells, a newly developed rat medullary thyroid carcinoma cell line. mRNA extracted from the cells directed the synthesis of a putative procalcitonin in a reticulocyte lysate translation system containing microsomal membranes. Both this species and a radiolabeled form of immunoreactive calcitonin from intact cells had the same retention time during reverse phase high performance liquid chromatography. The putative cellular procalcitonin was also immunoprecipitated by antiserum to a synthetic peptide whose sequence constitutes the COOH-terminal 16 residues of preprocalcitonin. The polypeptide had a Mr = 13,400, as estimated by gel filtration chromatography under denaturing conditions. Microsequencing of the [35S]methionine-labeled polypeptide indicated that residues 13, 32, and 34 of procalcitonin were methionine. Similar analysis of the peptide labeled with [3H]proline indicated that residues 2 and 11 of the precursor were proline. The positions of methionine and proline could be aligned in a unique manner with the NH2-terminal half of the preprocalcitonin sequence inferred from cDNA analyses. These results indicate that procalcitonin consists of 111 amino acids and suggest that a 25-residue signal sequence is cotranslationally cleaved from preprocalcitonin. From the procalcitonin sequence we can now predict the sequence of likely biosynthetic intermediates and mature secretory products derived from the NH2-terminal as well as COOH-terminal regions of the precursor.

The amino acid sequence of D-ribose-binding protein from Escherichia coli K12

The amino acid sequence of the D-ribose-binding protein from Escherichia coli K12 was determined from the DNA sequence of the gene. Protein sequence analyses covering 80% of the protein were consistent with the sequence deduced from the DNA. The mature binding protein has 271 amino acid residues and shows substantial homology to D-galactose-binding protein. A signal peptide sequence of 23 or 25 residues was also deduced from the DNA sequence. It shows the characteristic features of prokaryotic signal peptides.

The complete amino acid sequence of rabbit muscle phosphoglucomutase

The complete amino acid sequence of rabbit muscle phosphoglucomutase has been determined by isolating the 11 peptide fragments produced by the cyanogen bromide cleavage reaction and subjecting these to automated sequencing procedures. Products produced by treatment of some of these fragments with hydroxylamine, iodosobenzoic acid, mild acid, cyanogen bromide in formic and heptafluorobutyric acids, Staphylococcus aureus V8 protease, and trypsin (with or without blocking at lysine residues) were used to complete the sequence for each of the cyanogen bromide fragments. The cyanogen bromide fragments were ordered by isolating the four tryptic peptides produced by a limited tryptic digest of the native enzyme in the presence of its substrates and its bivalent metal ion activator, Mg2+, degrading these by means of trypsin, after blocking digestion at lysine residues, and isolating and identifying all fragments thus produced that contained 10 or more residues. The 561-residue sequence thus obtained is one of the longest that has been determined by chemical means. There is excellent agreement between this sequence and published compositions after appropriate normalization. The absorbance of the enzyme is about 7.0 at 278 nm for a 1% solution; this value is 9% lower than that previously used.

Inhibition of protein glycosylation and selective cytotoxicity toward virally transformed fibroblasts caused by B3-tunicamycin

The biological effect of B3-tunicamycin, the only known homologue of tunicamycin which contains a saturated fatty-acid side chain, was examined using chick embryo fibroblasts, a mouse fibroblastic line (3T3) and a virally transformed mouse fibroblastic line (SV40-3T3). This homologue inhibited the transfer of N-acetylglucosamine 1-phosphate from UDP-N-acetylglucosamine to dolichyl phosphate, catalyzed by microsomes from chick liver or from cultured mouse fibroblasts. B3-tunicamycin also inhibited the incorporation of mannose into glycoproteins synthesized by chick or mouse fibroblasts. Incorporation of the amino acids proline and tyrosine was inhibited by B3-tunicamycin to a lesser extent than the incorporation of mannose. The mannose incorporation into glycoproteins synthesized by virally transformed cells was inhibited by B3-tunicamycin to a higher degree than what was achieved in the nontransformed lines or in the chick primary fibroblasts. When the activity of B3-tunicamycin as an inhibitor of protein glycosylation was compared to other homologues of tunicamycin, it was found to be the most active. This homologue caused complete (more than 95%) inhibition of protein glycosylation at a concentration of 50 ng/ml in chick and in mouse fibroblasts and at a concentration of 10 ng/ml in transformed mouse fibroblasts. When the cytotoxic activities of tunicamycin homologues were examined on nontransformed and virally transformed 3T3 cells, it was found that B3-tunicamycin displayed the highest selective cytotoxicity toward the transformed cells. When transformed fibroblasts (10(5) cells/plate) were treated with B3-tunicamycin (100 ng/ml) for 48 h, complete cell death was observed. The viability and the proliferative activity of the nontransformed fibroblast were normal even when treated with concentrations up to 500 ng/ml of B3-tunicamycin. This suggests that B3-tunicamycin may be a suitable candidate for studies of tumor growth in animals.

Human hypoxanthine-guanine phosphoribosyltransferase. Complete amino acid sequence of the erythrocyte enzyme

The entire amino acid sequence of hypoxanthine-guanine phosphoribosyltransferase from human erythrocytes has been defined. Peptide fragments formed by cleavage at arginine, glutamic acid, and methionine residues were analyzed by Edman degradation or digestion with carboxypeptidase. The complete primary structure of human hypoxanthine-guanine phosphoribosyltransferase was established by sequence analysis of 17 peptide fragments, 15 of which were purified by reverse-phase high pressure liquid chromatography. The enzyme is 217 residues long with a molecular weight equal to 24,470. Mass spectroscopy indicated that the NH2-terminal alanine is acetylated.

Isolation of denatured proteins and peptides by high-performance liquid chromatography. Effect of different perfluorinated acids, column length and large-pore supports

The utilization of high-performance liquid chromatography for the isolation of peptides and proteins is extended by the demonstration that trifluoroacetic acid, pentafluoropropionic acid and heptafluorobutyric acid are effective peptide and protein solvents and as components of a mobile phase alter both the absolute and relative retention times of eluting peptides. In addition, studies related to stationary-phase performance indicate that: (1) column length (5-25 cm) does not significantly influence large peptide or protein retention times or resolution; (2) 300 A pore supports are ideal for the isolation of both large peptides and proteins; (3) peptide and protein conformation, even in the presence of denaturants, alters the steric interaction with the support; and (4) large peptides and proteins probably interact with the support by virtue of multi-site binding, not partitioning between the stationary and mobile phases.

Relationship of the structure and biological activity of the natural homologues of tunicamycin

The antibiotic tunicamycin was separated into 16 different components using reversed-phase high performance liquid chromatography. The effect of the eight major tunicamycin homologues on protein glycosylation and protein biosynthesis was examined. All homologues tested inhibited lipid-mediated protein glycosylation in chick or mouse fibroblasts. These homologues also inhibited the transfer of N-acetylglucosamine-1-phosphate from UDP-N-acetylglucosamine to dolichyl phosphate in chick liver microsome preparations, whereas the transfer of mannose from GDP-mannose to the lipid acceptor was hardly affected. The inhibition of protein glycosylation in fibroblasts or in microsomal preparations was concentration-dependent and maximum inhibition occurred at different concentrations for different homologues. The eight homologues differed in their ability to cause inhibition of protein synthesis.

Structural prediction of sugar-binding proteins functional in chemotaxis and transport

Comparisons of the D-galactose- and D-ribose-binding protein amino acid sequences and secondary structure predictions with the known primary and three-dimensional structure of L-arabinose-binding protein suggest that the three proteins have similar molecular structures. These studies also indicate an evolutionary relationship among the proteins. One region of striking homology between the galactose- and ribose-binding proteins suggests that this may be th protein-protein contact site for interaction with the membrane-bound chemotaxis receptor. The ligands and the geometry of the galactose binding site are also predicted.

The amino acid sequence of the D-galactose-binding protein from Escherichia coli B/r

The complete primary structure of the Escherichia coli B/r galactose-binding protein was determined by the automated sequencing of fragments produced by cleavage with cyanogen bromide, o-iodosobenzoic acid, limited trypsin digestion, mild acid hydrolysis, and Staphylococcus aureus strain V8 protease. The protein, which has 309 amino acids, is notable in the extent to which it differs from the L-arabinose-binding protein. Comparison of these two proteins indicates only about 18% homology despite the close structural resemblence of the molecules which they bind. The galactose-binding protein is the chemoreceptor initiating chemotaxis toward galactose, and it thus becomes the first protein component required for chemotaxis for which the primary structure is known. GM 24602

Reversed-phase supports for th resolution of large denatured protein fragments

Large pore (much greater than 300 A), spherical partical silica stationary phases possessing either C18 or C8 hydrocarbon ligands out-performed small pore (60-100A), irregular shaped silicas for the purification of large denatured peptides. Since columns 5 cm in length appeared to be as effective in separating peptides as columns 5 times longer, it is likely that large peptides absorb to the matrix rather than partition between the stationary and mobile phases.

Fragmentation of proteins with o-iodosobenzoic acid: chemical mechanism and identification of o-iodoxybenzoic acid as a reactive contaminant that modifies tyrosyl residues

o-Iodoxybenzoic acid, a disproportionation product of o-iodosobenzoic acid, has been identified as a contaminant in most preparations of o-iodosobenzoic acid capable of both modifying and cleaving certain tyrosyl residues. A new synthetic approach for the production of o-iodosobenzoic acid containing low amounts of o-iodoxybenzoic acid combined with preincubation of the reagent with p-cresol to destroy the remaining o-iodoxybenzoic acid prior to the reaction with a polypeptide allows preparation of reagent solutions in which tyrosyl residues remain intact during tryptophanyl bond cleavage. In addition, the product produced by the action of o-iodosobenzoic acid upon tryptophanyl bonds has been identified as N-acyldioxindolylalanine. It is inferred from that structure that the chemical reaction proceeds via a two-step oxidation of the tryptophanyl residue followed by formation of an iminospirolactone which hydrolyzes, cleaving the peptide chain. Small peptides ending with dioxindolylalanine can be coupled to aminopropyl glass in high yield and are suitable for solid-phase Edman degradation.

Separation of large denatured peptides by reverse phase high performance liquid chromatography. Trifluoroacetic acid as a peptide solvent

A method employing reverse phase high performance liquid chromatography has been developed for the purification of large denatured peptides. The cyanogen bromide fragments of hemoglobin alpha, beta, and gamma chains (13 to 91 residues in length) could be separated and recovered in 71 to 95% yields using LiChrosorb C-8 columns and a binary solvent system consisting of 0.013 M trifluoroacetic acid in water and a limiting organic solvent. This procedure permits the nondestructive detection of peptides at low wavelength (210 nm) on as little as 50 ng of sample. The peptides are recovered directly by evaporation or lyophilization. An elutropic solvent series for the separation of large and small peptides on reverse phase supports is also described.

Fetal hemoglobin of the rhesus monkey, Macaca mulatta: complete primary structure of the gamma chain

The complete amino acid sequence of the gamma chain from the major one of two fetal hemoglobins from the rhesus monkey, Macaca mulatta, was determined by automated, stepwise degradation of selected fragments produced by cleavage at methionyl and tryptophanyl residues and at the single aspartylprolyl bond. The minor fetal hemoglobin is single aspartylprolyl bond. The minor fetal hemoglobin is similar to human Hb F1 in relative electrophoretic and chromatographic properties and in the level at which it is found (about 12% of the total Hb F). On these grounds, we assume that this minor component contains, like Hb FI, gamma chains that differ from those of the major component by virtue of acetylation of their amino-terminal glycyl residues. Although the gamma chains of most antropoid primates examined to date are structurally heterogeneous and, hence, appear to be encoded by nonallelic genes, no sign of structural heterogeneity was detected at any position in the major gamma chain from M. mulatta. Thus, if nonallelic gamma-chain genes exist in this species, the chains encoded by them may be identical in sequence. The gamma chain from M. mulatta is but the sixth primate gamma chain whose primary structure has been fully characteerized. The slight extent of structural divergence among these chains (the four chains from various species of Old World monkeys differ from one another by no more than two substitutions, while the human and cercopithecoid gamma chains differ at no more than five sites) attests to the conservative nature of gamma-chain evolution among the higher primates.

Formation and dissociation of the covalent complexes between trypsin and two homologous inhibitors, alpha 1-antitrypsin and antithrombin III

The mechanisms by which alpha 1-antitrypsin and antithrombin III inhibit trypsin were investigated by chemical stability studies and amino acid sequence analyses of the enzyme-inhibitor complexes. One-to-one covalently linked complexes were formed between each of the inhibitors and trypsin. The complexes were stable over the course of the experiments at pH 8 or lower, and benzamidine, hydroxylamine, thiols, guanidine, or dodecyl sulfate had no apparent effect on the stability of the complexes. The complexes dissociated slowly at pH 9 or greater. Neither of the inhibitors was active after dissociation from its complex with trypsin. Sequence analysis indicated that no new amino terminus was generated when alpha 1-antitrypsin formed its complex with trypsin, but that two new amino termini were formed in approximately one-to-one ratio when the complex dissociated. This may indicate that alpha 1-antitrypsin contains two inhibitory sites for trypsin in close spatial proximity on the molecule.

Complete primary structure of the beta chain from the hemoglobin of a baboon, Papio cynocephalus

The complete primary structure of the beta chain from the adult hemoglobin of a baboon, Papio cynocephalus, has been determined by automated, Edman degradation of the intact chain and four fragments derived therefrom by specific cleavage reactions. The analysis was facilitated by application of a modified solvent system that permits unambiguous identification, by high-performance liquid chromatography, of the 17 amino acids whose phenylthiohydantoin derivatives are soluble in ethyl acetate. The sequence obtained differs from that of the human beta chain at eight sites, a degree of divergence similar to that observed when human and macaque beta chains are compared. Of the cercopithecoid beta chains whose complete sequences have been determined or inferred from compositions of small peptides, that of P. cynocephalus is most like the beta chain of the gelada baboon, an observation in accord with assessment of a close phylogenetic relationship between the genera Papio and Theropithecus.

High-yield cleavage of tryptophanyl peptide bonds by o-iodosobenzoic acid

A new procedure to cleave tryptophanyl peptide bonds in high yield is reported. The method involves treatment of the S-alkylated protein with o-iodosobenzoic acid. The procedure is highly selective for tryptophan and does not modify tyrosine or histidine, but may convert methionine to its sulfoxide derivative. The yields in the cleavage are 70--100%. Tryptophanyl bonds to alanine, glycine, serine, threonine, glutamine, arginine, and S-(pyridylethyl)cysteine are split in nearly quantitative yield, while those preceding isoleucine or valine are split in approximately 70% yield in the proteins examined in this work. The chemical mechanism for tryptophanyl bond cleavage has not been defined, but it is likely that oxidation of the indole ring occurs during the reaction with o-iodosobenzoic acid. Some problems with the quality of commercial preparations of the reagent are discussed.

Biological activities of the two major components of tunicamycin

Tunicamycin, an antibiotic that inhibits the transfer of N-acetyglucosamine-1-phosphate from UDP-N-acetylglucosamine to dolichol monophosphate and thereby blocks the formation of protein-carbohydrate linkages of the N-glycosidic type, is not a single compound but a mixture of homologous antibiotics. Two major and eight minor homologs have been identified, all of which possess the ability to inhibit protein glycosylation. The biological activities of the two major components of tunicamycin were investigated and found to differ in their ability to inhibit protein glycosylation and in their effectiveness to inhibit protein synthesis. When completely blocking mannose incorporation into protein, one homolog inhibited protein synthesis by 50% while the other had only a negligible effect. The results demonstrate that differences in biological activity can be discriminated among tunicamycin homologs.

Complete amino acid sequence of the gamma chain from the major fetal hemoglobin of the pig-tailed macaque, Macaca nemestrina

The complete primary structure of the gamma chain of the major fetal hemoglobin from the pig-tailed macaque, Macaca nemestrina, was obtained by the automated sequencing of fragments produced by three nonenzymatic cleavage reactions. About two-thirds of the sequence was established from the amino terminus of the intact chain and two of the three fragments produced by cleavage at methionyl residues by cyanogen bromide. Acid clevage at the single aspartyl-prolyl linkage and cleavage at tryptophanyl residues in intact chains yielded the two fragments necessary to complete the sequence. This gamma chain, the first from a nonhuman primate to be sequenced, differes from the human G gamma and A gamma chains at but 4 and 5 positions, respectively. All substitutions are conservative and unlikely to produce alterations in the oxygen-binding properties of tetrameric fetal hemoglobin. Consideration of the data presented herein, together with published observations made on portions of other primate gamma chains, provides some insight into the evolutionary history of the multiple gamma-globin chains observed in several anthropoid primates.