4-NN-dimethylaminoazobenzene 4''-isothiocyanate, a new chromophoric reagent for protein sequence analysis.

4-NN-Dimethylaminoazobenzene 4'-isothiocyanate was synthesized for the purpose of improving the ease and sensitivity of peptide sequence analysis. The method of 4-NN-dimethylaminoazobenzene 4'-isothiocyanate synthesis, the preparation of 24 4-NN-dimethylaminoazobenzene-4'-thiohydantoins of amino acids and their t.l.c. separation are described. All the thiohydantoins, except those of leucine and isoleucine, could be satisfactorily separated by chromatography on a two-dimensional polyamide sheet. The sensitive azo group permits the detection of 4-NN-dimethylaminoazobenzene-4'-thiohydantoins of amino acids as red spots down to pmol amounts directly on the sheet. A simple sensitive method for sequencing dipeptides and the first two or three N-terminal amino acids of proteins is also reported. The colour change of the spots from purple to blue to red after being exposed to HCl vapour, corresponding to the chemical change from 4-NN-dimethylaminoazobenzene-4' isothiocyanate to the 4-NN-dimethylaminoazobenzene-4'-thiocarbamoyl amino acid derivative to the 4-NN-dimethylaminoazobenzene-4'-thiohydantoin amino acid derivative, reveals a very interesting and valuable feature of this reagent.     

High-sensitivity sequence analysis of peptides and proteins by 4-NN-dimethylaminoazobenzene 4''-isothiocyanate.

A manual high-sensitivity sequencing method is described, in which 4-NN-dimethylaminoazobenzene 4'-isothiocyanate is used for the stepwise degradation of amino acid residues from the peptides. The 4-NN-dimethylaminoazobenzene 4'-thiazolinones of amino acids that were released, after conversion into their thiohydantoin derivatives, were identified by t.l.c. on polyamide sheets. This new method is simple and sensitive, and requires only 2-10nmol of peptides or proteins for extended sequence analysis. The method was tested on the sequence analysis of a hexapeptide (Leu-Trp-Met-Arg-Phe-Ala), bradykinin, glucagon and native lysozyme. Results show that the proposed procedure is a sensitive method for the sequence determination of short peptides as well as for the partial sequence determination of intact proteins.     

Manual solid phase sequence analysis of polypeptides using 4-N-N,-dimethylaminoazobenzene 4'-isothiocyanate.

A manual solid-phase method for sequence analysis of polypeptides is described. The immobilized polypeptide was subjected to stepwise degradation by Edman-type reagent, using the 4-N,N-dimethylaminoazobenzene 4'-isothiocyanate phenyllisothiocyanate double coupling method. The N-terminal amino acids were released (after conversion reaction) as 4-N,N-dimethylaminoazobenzene 4'-thiohydantoin (identified by thin layer chromatography) and phenylthiohydantoin derivatives. The method required 2--10 nmol polypeptide.     

Monitoring of environmental cancer initiators through hemoglobin adducts by a modified Edman degradation method

Tissue doses of cancer initiators/mutagens are suitably monitored through hemoglobin adducts formed in vivo, but the use of this method has been hampered by a lack of sufficiently simple and fast procedures. It was previously observed that when the N-terminal amino acid in hemoglobin, valine, is alkylated it is cleaved off by the Edman sequencing reagent, phenyl isothiocyanate, in the neutral-alkaline coupling medium, as opposed to the acidic medium required by normal amino acids. Based on this principle, conditions for a functioning procedure for gas chromatography/mass spectrometry (GC/MS) determination of N-terminal alkylvalines in hemoglobin were worked out. Derivatizing the protein in formamide solution with pentafluorophenyl isothiocyanate, using a 2H-alkylated protein as internal standard, and applying on-column injection during analysis, permit reproducible determination of hydroxyethylvaline and other adducts down into the dose range where cancer risks may be considered acceptably low.     

Covalent immobilization of proteins for high-sensitivity sequence analysis: electroblotting onto chemically activated glass from sodium dodecyl sulfate-polyacrylamide gels

We report a new method for the preparation of proteins in a form suitable for high-sensitivity N-terminal amino acid sequence analysis. Proteins separated by polyacrylamide gel electrophoresis were electrophoretically transferred onto glass fiber filter paper chemically activated by the introduction of phenyl isothiocyanate functional groups. The proteins became covalently coupled to the matrix during the electrotransfer process. Bands containing transferred proteins were detected by fluorescent staining or autoradiography, cut out from the glass fiber filter, and directly loaded into the cartridge of a gas-phase sequenator. The covalent nature of the interactions between protein and glass fiber support permitted the use of more vigorous solid-phase sequencing protocols and of alternative sequencing reagents. This high-efficiency isolation and covalent coupling method provides the essential first step toward enhanced-sensitivity protein sequence analysis. The method has been successfully applied to the isolation of a wide variety of proteins from SDS-polyacrylamide gels, and was shown to be compatible with both the standard Edman reagent phenyl isothiocyanate and alternative sequencing reagents such as 4-(N,N'-dimethylamino)azobenzene-4'-isothiocyanate (DABITC).     

Localization of the N-terminal methionine of rat liver cytochrome P-450 in the lumen of the endoplasmic reticulum

Recent cumulative evidence suggests that liver microsomal cytochrome P-450 (P-450) is exposed to the cytosol with the exception of the N-terminal peptide (amino acid residues 1 to 21), or two peptides (residues 1 to 60). We tested the localization of the N-terminal methionine residue of P-450IIB1 of rat liver microsomes in the natural membrane with the site-specific reagent fluorescein isothiocyanate. The N-terminus of isolated P-450 was stoichiometrically modified in solution with fluorescein isothiocyanate. In intact microsomes, the N-terminus was not modified but became accessible to the reagent when the membrane was dissolved with Triton X-100. Our results indicate that the N-terminus faces the lumen of the endoplasmic reticulum, and we propose that P-450 spans the membrane only once with amino acid residues 1 to 21.     

Application of amino acid analysis by high-performance liquid chromatography with phenyl isothiocyanate derivatization to the rapid determination of free amino acids in biological samples

An amino acid analysis by reversed-phase high-performance liquid chromatography after precolumn derivatization with phenyl isothiocyanate was adapted to the determination of free amino acids in plasma or other biological fluids and in tissue homogenates. Preparation of samples included deproteinization by 3% sulphosalicylic acid, and careful removal under high vacuum of residual phenyl isothiocyanate after derivatization. A Waters Pico-Tag column (15 cm long) was used, immersed in a water-bath at 38°C. In rat or human plasma, separation of 23 individual amino acids, plus the unresolved pair tryptophan and ornithine, was obtained within 13 min. Including the time for column washing and re-equilibration, samples could be chromatographed at 23-min intervals. Variability was tested for each amino acid by calculating the coefficients of variation of retention times (less than 1% in the average) and peak areas (less than 4% for both intra-day and inter-day determinations). The linearity for each standard amino acid was remarkable over the concentration range 3–50 nmol/ml. The mean recovery of amino acid standards added to plasma prior to derivatization was 97 ± 0.8%, except for aspartate (82%) and glutamate (81%). This method is rapid (almost three samples per hour can be analysed, more than in any other reported technique), with satisfactory precision, sensitivity and reproducibility. Therefore, it is well suited for routine analysis of free amino acids in both clinical and research work.     

Identification of amino acid thiohydantoins directly by thin-layer chromatography and indirectly by gas-liquid chromatography after hydrolysis.

A method is described for the identification of amino acid thiohydantoins by two-dimensional t.l.c. An indirect method for the determination of amino acid thiohydantoins is described which, after hydrolysis, the corresponding amino acids are determined by g.l.c.     

A peptide released from plasma fibrin stabilzing factor in the conversion to the active enzyme by thrombin

A peptide, which was released accompanying with the activation of bovine plasma fibrin stabilizing factor (FSF) by thrombin, was isolated and characterized. The peptide consisted of Asp4, Thr₃, Ser₄, Glu₄, Pro₅, Gly₄, Ala₄, Val₂, Ile₁, Leu₂, Phe₁, and Arg₃. The content of proline was highest in all of these amino acids. The carboxyl-terminal residue of the peptide was identified as arginine. However, no N-terminal amino acid reactive with phenyl$\text{iso}$thiocyanate and dansyl chloride could be determined. Edman degradation on the inactive FSF showed glutamic acid or glutamine as one N-terminal residue. After the activation of FSF by thrombin, glycine was identified as a second N-terminal residue, in addition to glutamic acid (glutamine).These results indicate that the transformation of FSF to the active enzyme by thrombin involves proteolysis of an arginyl-glycyl bond located in the N-terminal region of one of the subunits of the proenzyme.     

Qualitative determination of N-terminal amino acids of peptides and proteins with cobalt(III) chelates

1. A method of N-terminal peptide-bond hydrolysis with the cis-beta-hydroxyaquo(triethylenetetramine)cobalt(III) ion, i.e. beta-[Co(trien)(OH)(OH(2))](2+), is reported. The method has been demonstrated with 22 small peptides and ten proteins. 2. The procedure is rapid (an N-terminal amino acid determination can be made easily in one day), it involves no acid hydrolysis step and thus no destruction of labile amino acids, and it involves the use of easily prepared inexpensive reagents. 3. The released N-terminal amino acids can be identified as their cobalt(III) derivatives, or directly as the amino acid or as their dansylated derivatives. 4. The method is to treat 1 mumol of peptide or protein with beta-[Co(trien)(OH)(OH(2))](2+) reagent at pH8.0, 45 degrees C for 3h. Addition of 0.5m-phosphate buffer, pH10.5 at 45 degrees C for 10min cleaves the N-terminal bidentate amino acid-cobalt complex, which can be identified directly. For greater sensitivity with 10nmol of peptide) the free amino acid is prepared from the complex by treatment (with NaCN (0.1m, 40 degrees C, 30min), or H(2)S or NaBH(4) (25 degrees C, 5min), dried, dansylated and the dansyl-amino acid identified by high-voltage electrophoresis. The method is unaffected by the presence of 4-8m-urea, but will not cleave blocked N-terminal acids.     

Automated simultaneous isolation and quantitation of labeled amino acid fractions from plasma and tissue by ion-exchange chromatography

In order to trace metabolic pathways of amino acids in the body, a known labeled amount of an amino acid is infused. Dilution in the body pool is measured, using the specific activity and calculated by dividing the labeled amount of an amino acid (tracer) by its total pool (tracer + tracee). This paper describes a method, which combines fractionation and quantitation of multiple amino acids in one chromatographic run. To achieve this, we performed a classical amino acid ion-exchange separation on standard HPLC equipment. The column effluent was divided continuously into two solvent streams using a rapidly switching, pump controlled “split-valve”. The main part (90%) was directed to a computer controlled fraction collector, while the remaining 10% was mixed with o-phthaldialdehyde reagent after which fluorescence was measured. Using this system, 10–1000 μl of deproteinized plasma, representing a maximum of 50 nmol of each amino acid, could be fractionated and quantitated in the same chromatographic run. In addition to optimal counting efficiency of an off-line radioactivity counter, it enabled easy measurement of the specific activity of multiple amino acid tracers.     

The N-terminal region of the transmembrane domain of human erythrocyte band 3. Residues critical for membrane insertion and transport activity

We studied the role of the N-terminal region of the transmembrane domain of the human erythrocyte anion exchanger (band 3; residues 361-408) in the insertion, folding, and assembly of the first transmembrane span (TM1) to give rise to a transport-active molecule. We focused on the sequence around the 9-amino acid region deleted in Southeast Asian ovalocytosis (Ala-400 to Ala-408), which gives rise to nonfunctional band 3, and also on the portion of the protein N-terminal to the transmembrane domain (amino acids 361-396). We examined the effects of mutations in these regions on endoplasmic reticulum insertion (using cell-free translation), chloride transport, and cell-surface movement in Xenopus oocytes. We found that the hydrophobic length of TM1 was critical for membrane insertion and that formation of a transport-active structure also depended on the presence of specific amino acid sequences in TM1. Deletions of 2 or 3 amino acids including Pro-403 retained transport activity provided that a polar residue was located 2 or 3 amino acids on the C-terminal side of Asp-399. Finally, deletion of the cytoplasmic surface sequence G(381)LVRD abolished chloride transport, but not surface expression, indicating that this sequence makes an essential structural contribution to the anion transport site of band 3.     

Protein pico-sequencing with 4-([5-(dimethylamino)-1-naphthylsulfonyl]amino) phenyl isothiocyanate

A novel manual liquid phase protein sequencing method using the fluorescent reagent, 4-([5-(dimethylamino)-1-naphthylsulfonyl] amino) phenyl isothiocyanate proposed by Jin et al. (FEBS Lett. 198, 150, 1986) has been established. This method allowed sequence determination using 100 pmol and 1 nmol of insulin B chain (oxidised) for 9 and 19 cycles respectively with thin-layer chromatographic identification of the fluorescent thiohydantoin amino-acid derivatives. The method compares favorably in sensitivity with other conventional manual protein sequencing methods.     

Octapeptide repeat region and N-terminal half of hydrophobic region of prion protein (PrP) mediate PrP-dependent activation of superoxide dismutase

Cellular prion protein PrP(C) contains two evolutionarily conserved domains among mammals; viz., the octapeptide repeat region (OR; amino acid residue 51-90) and the hydrophobic region (HR; amino acid residue 112-145). Accumulating evidence indicates that PrP(C) acts as an inhibitor of apoptosis and regulator of superoxide dismutase (SOD) activity. To further understand how PrP(C) activates SOD and prevents apoptosis, we provide evidence here that OR and N-terminal half of HR mediate PrP(C)-dependent SOD activation and anti-apoptotic function. Removal of the OR (amino acid residue 53-94) enhances apoptosis and decreases SOD activity. Deletion of the N-terminal half of HR (amino acids residue 95-132) abolishes its ability to activate SOD and to prevent apoptosis, whereas that of the C-terminal half of HR (amino acids residue 124-146) has little if any effect on the anti-apoptotic activity and SOD activation. These data are consistent with a model in which the anti-apoptotic and anti-oxidative function of PrP(C) is regulated by not only OR but also the N-terminal half of HR.     

A study of the interaction of 2-p-isothiocyanphenyl-3-phenylindone with peptides and proteins

The conditions of interaction with peptide chains of a new reagent for determination of amino acid sequence—2-p-isothiocyanophenyl-3-phenylindone—were established. The conditions for cleavage of the N-terminal amino acid as a colored diphenylindonyl-substituted thiohydantoin derivative were found as well. λ_max and ε_max of diphenylindonyl thiohydantoin derivatives of all common amino acids usually found in proteins were determined. ε_max values are about three times higher than the corresponding values of phenylthiohydantoin derivatives.     

N-terminal sequence analysis of polypeptide at the picomole level.

This paper describes a manual method for N-terminal sequence analysis of polypeptides at subnanomole sensitivity. The polypeptide is degraded stepwise by using the dimethylaminoazobenzene isothiocyanate/phenyl isothiocyanate double-coupling method, and the released dimethylaminoazobenzenethiohydantoins of amino acids were identified by reversed-phase high-pressure liquid chromatography. The dimethylaminoazobenzenethiohydantoins are coloured compounds and can be detected in the visible region with the sensitivity limit of 1 pmol (signal-to-baseline noise ratio 5). A high-pressure liquid-chromatographic method was developed for complete analysis of all amino acid dimethylaminoazobenzenethiohydantoin derivatives, including the by-products of serine and threonine. Thus, without use of an automatic sequenator or radioactive materials, it is possible to determine the complete sequence of peptides and N-terminal sequence of proteins with less than 1 nmol of material.     

A manual subtractive end-group determination of oligopeptides using fluorescamine or o-phthalaldehyde

A new method for the end-group determination of peptides using the fluorogenic reagents fluorescamine or o-phthalaldehyde is described. The method is based on the property that the derivatives of the N-terminal amino group of peptides formed in solution after reaction with either reagent are resistant to acid hydrolysis. The N-terminal amino acid can be determined by simply comparing the amino acid analysis of the original peptide with the fluorescent derivative of the peptide. In general, the decrease of the N-terminal residue in the reacted peptides in 80–90% with fluorescamine and more than 90% with o-phthalaldehyde. Any N-terminal amino acid, with the exception of proline, can thus be determined.     

Glutathionylation of lens proteins through the formation of thioether bond

Formation of lanthionine, a dehydroalanine crosslink, is associated with aging of the human lens and cataractogenesis. In this study we investigated whether modification of lens proteins by glutathione could proceed through an alternative pathway: that is, by the formation of a nonreducible thioether bond between protein and glutathione. Direct ELISA of the reduced water-soluble and water-insoluble lens proteins from human cataractous, aged and bovine lenses showed a concentration-dependent immunoreactivity toward human nonreducible glutathionyl-lens proteins only. The reduced water-insoluble cataractous lens proteins showed the highest immunoreactivity, while bovine lens protein exhibited no reaction. These data were confirmed by dot-blot analysis. The level of this modification ranged from 0.7 to 1.6 nmol/mg protein in water-insoluble proteins from aged and cataractous lenses. N-terminal amino acid determination in the reduced and alkylated lens proteins, performed by derivatization of these preparations with dansyl chloride followed by an exhaustive dialysis, acid hydrolysis and fluorescence detection of dansylated amino acids by RP-HPLC, showed that N-terminal glutamic acid was present in concentration of approximately 0.2 nmol/mg of lens protein. This evidence points out that at least some of the N-terminal amino groups of nonreducible glutathione in the reduced human lens proteins are not involved in a covalent bond formation. Since disulfides were not detected in the reduced and alkylated human lens proteins, GSH is most likely attached to lens proteins through thioether bonds. These results provide, for the first time, evidence that glutathiolation of human lens proteins can occur through the formation of nonreducible thioether bonds.     

Isolation of a specific granulopoiesis inhibitor from calf spleen and identification as glutathione

A small peptide was isolated from calf spleen, specifically inhibiting murine granulopoiesis in vitro. Purification involved ultrafiltration, anion-exchange chromatography with a FPLC system and reversed-phase chromatography on HPLC. Determination of the amino acid composition, following acid hydrolysis and phenyl isothiocyanate and dabsyl chloride derivatization, revealed the amino acids glutamic acid, cysteine and glycine. Although the N-terminal amino group was not blocked, peptide sequencing with common techniques was not possible. Comparison of the isolated peptide with the well-known tripeptide glutathione by HPLC and fast atom bombardment (FAB)/tandem mass spectrometry showed the identity of both substances. Moreover, glutathione was found to be a specific granulopoiesis inhibitor in vitro at 10-100 nM, a so far unknown property of this well-known peptide.     

The N-terminal amino acid sequence of plastocyanin from Stellaria media L. An exercise to establish criteria for the identification of residues from a sequenator.

The N-terminal amino acid sequence of plastocyanin from Stellaria media L. (chickweed) has been determined by means of an automatic sequencer. Amino acid derivatives obtained during the degradation were identified by a combination of t.l.c., g.l.c. and regeneration of the parent amino acid. The analytical results are presented for each sample, and the criteria used to establish the amino acid sequence are discussed.