Amino acid analysis: determination of cysteine plus half-cystine in proteins after hydrochloric acid hydrolysis with a disulfide compound as additive

Determination of the disulphide bridge arrangement of bovine histidine-rich glycoprotein

Histidine-rich glycoprotein (HRG) was purified from bovine plasma and the disulphide bridge arrangement established. Disulphide-bridged peptides were obtained from peptic and tryptic degradation of native bovine HRG. Twelve half-cystine residues were found in bovine HRG (compared to sixteen cysteines in human HRG), all involved in the formation of six disulphide bridges connecting Cys-1 to Cys-12, Cys-2 to Cys-3, Cys-4 to Cys-5, Cys-6 to Cys-11, Cys-7 to Cys-8, and Cys-9 to Cys-10. Additional sequence analysis of 14C-carboxymethylated chymotryptic and Staphylococcus aureus V8 protease generated peptides and CNBr-fragments of bovine HRG yielded a partial amino acid sequence of bovine HRG constituting 78% of the sequence when compared to the human cDNA sequence.

Amino acid sequences of ovomucoid third domains from 27 additional species of birds

Ovomucoids consist of a single polypeptide chain which is composed of three tandem Kazal domains. Each Kazal domain is an actual or putative protein inhibitor of serine proteinases. Ovomucoid third domains were already isolated and sequenced from 126 species of birds (Laskowski et al., 1987, 1990). This paper adds 27 new species. A number of generalizations are made on the basis of sequences from 153 species. The residues that are in contact with the enzyme in enzyme-inhibitor complexes are strikingly hypervariable. While the primary specificity residue, P1, is the most variable; substitutions occur predominantly among aliphatic, hydrophobic residues. Consensus sequences for an avian ovomucoid third domain, for a b-type Kazal domain (i.e., a COOH terminal domain of multidomain inhibitors) and for a general Kazal domain are given. Finally, the individual new sequences are briefly discussed.

Purification and characterization of three proteins isolated from the proteose peptone fraction of bovine milk

Three major proteins from the proteose peptone of bovine milk were purified by Sephadex G-75 gel chromatography, Q-Sepharose ion-exchange and additional Sephadex G-75 gel chromatography in the presence of urea. From their mobility in a gradient SDS-PAGE, the proteins were found to have molecular masses of 17, 28 and 60 kDa. The N-terminal amino acid sequence of the 17 kDa protein was found to be homologous with a camel whey protein. This protein has not previously been described in bovine milk. From the SDS-PAGE results, the 28 kDa protein was judged to be the major protein of proteose peptone, contributing approximately 25% of the total. The N-terminal amino acid sequence showed no homology to any known protein sequence, but the amino acid composition indicated that the 28 kDa protein is identical with the PP3 component from the proteose peptone fraction of bovine milk, or part of it. The 60 kDa protein was found to be bovine osteopontin, a very highly phosphorylated protein with an Arg-Gly-Asp sequence which mediates cell attachment.

Amino acid sequence of Coprinus macrorhizus peroxidase and cDNA sequence encoding Coprinus cinereus peroxidase. A new family of fungal peroxidases

Sequence analysis and cDNA cloning of Coprinus peroxidase (CIP) were undertaken to expand the understanding of the relationships of structure, function and molecular genetics of the secretory heme peroxidases from fungi and plants. Amino acid sequencing of Coprinus macrorhizus peroxidase, and cDNA sequencing of Coprinus cinereus peroxidase showed that the mature proteins are identical in amino acid sequence, 343 residues in size and preceded by a 20-residue signal peptide. Their likely identity to peroxidase from Arthromyces ramosus is discussed. CIP has an 8-residue, glycine-rich N-terminal extension blocked with a pyroglutamate residue which is absent in other fungal peroxidases. The presence of pyroglutamate, formed by cyclization of glutamine, and the finding of a minor fraction of a variant form lacking the N-terminal residue, indicate that signal peptidase cleavage is followed by further enzymic processing. CIP is 40-45% identical in amino-acid sequence to 11 lignin peroxidases from four fungal species, and 42-43% identical to the two known Mn-peroxidases. Like these white-rot fungal peroxidases, CIP has an additional segment of approximately 40 residues at the C-terminus which is absent in plant peroxidases. Although CIP is much more similar to horseradish peroxidase (HRP C) in substrate specificity, specific activity and pH optimum than to white-rot fungal peroxidases, the sequences of CIP and HRP C showed only 18% identity. Hence, CIP qualifies as the first member of a new family of fungal peroxidases. The nine invariant residues present in all plant, fungal and bacterial heme peroxidases are also found in CIP. The present data support the hypothesis that only one chromosomal CIP gene exists. In contrast, a large number of secretory plant and fungal peroxidases are expressed from several peroxidase gene clusters. Analyses of three batches of CIP protein and of 49 CIP clones revealed the existence of only two highly similar alleles indicating less peroxidase polymorphism in C. cinereus strains than observed in plants and white-rot fungi.

Procathepsin D cannot autoactivate to cathepsin D at acid pH

The amino acid sequence of the propart of bovine procathepsin D was determined at the protein level. Incubation of the isolated procathepsin D at pH 3.5-5.0 for 30-120 min leads to a 2 kDa reduction in its molecular mass, as seen by SDS-PAGE. The activation product is pseudocathepsin D and is the result of a proteolytic cleavage between LeuP26 and IleP27 in the propart. Incubation at pH 5.0 for 20 h of either procathepsin D or pseudocathepsin D results in both cases in approximately equal amounts of pseudocathepsin D and a further processed intermediate, nine amino acids shorter than pseudocathepsin D. No reaction products corresponding to cathepsin D with a mature amino terminus were observed, showing that autoproteolysis alone cannot generate the mature form found in the lysosomes.

Evidence from sequence analysis that hen egg-white ovomacroglobulin (ovostatin) is devoid of an internal beta-Cys-gamma-Glu thiol ester

53 residues of the internal sequence from the proteinase-binding hen egg-white ovostatin have been determined. The stretch corresponds to residues 945-997 of human alpha 2-macroglobulin. The degree of conservation of residues of the two stretches is approx. 74%. Cys-949, being one constituent of the internal thiol ester site of members of the family of proteins related to alpha 2-macroglobulin, is an Asn-residue in hen egg-white ovostatin, but the other constituent, Gln-952, is preserved. The Cys-to-Asn substitution forms the chemical basis for the lack of thiol esters in hen egg-white ovostatin.

Solid-phase peptide synthesis on proteins

A new method for solid-phase peptide synthesis in which a protein is used as the solid support has been developed. Two aspects of the method have been demonstrated. The peptides H-Phe-Leu-Glu-Glu-Val-OH (1) and H-Leu-Leu-Ala-Gly-Val-OH (2), respectively, were synthesized on the amino groups of BSA via a cleavable linker, using the Fmoc group protecting scheme. The free peptides were obtained by cleavage from the protein with 95% TFA, precipitation in diethyl ether and additional work-up by either dialysis or centrifugation through a membrane followed by gel filtration. The identity of the products was determined by amino acid analysis and HPLC. The peptide-protein conjugates, H-Ser-Met-Asp-Thr-Ser-Asn-Lys-Glu-Glu-Lys-BSA (3) and H-Thr-Val-Leu-BTG (4), were obtained in the same manner, omitting the cleavable linker group. It was found that 35-50 peptide chains were conjugated per molecule BSA and BTG, respectively. Immunization of rabbits with conjugate 3 gave rise to peptide specific antibodies. This method will be useful for generation of sequence specific antibodies, since the peptide is conjugated to the carrier protein exclusively via its C-terminus, and will allow synthesis of highly specific peptide-protein conjugates.

Disulfide bridges in human complement component C3b

The disulfide bridges of human complement component C3b, derived from C3 by removal of the 77-residue C3a, have been determined. The 10 bridges are Cys537-Cys794, Cys605-Cys640, Cys851-Cys1491, Cys1079-Cys1136, Cys1336-Cys1467, Cys1367-Cys1436, Cys1484-Cys1489, Cys1496-Cys1568, Cys1515-Cys1639, and Cys1615-Cys1624. Including the 3 bridges in C3a (Cys670-Cys698, Cys672-Cys705, and Cys685-Cys706) previously determined by high-resolution X-ray crystallography [Hoppe-Seyler's Z. Physiol. Chem. 361 (1980) 1389-1399] all disulfide bridges of C3 are localized. C3 and the strongly related C4 and C5 are members of the alpha 2-macroglobulin superfamily. The predicted bridge patterns of C4 and C5 are discussed and compared with that of alpha 2-macroglobulin.

Primary structure of the major isomorph of the crustacean hyperglycemic hormone (CHH-I) from the sinus gland of the Mexican crayfish Procambarus bouvieri (Ortmann): interspecies comparison

The amino acid sequence of this neuropeptide was elucidated by means of a combined approach of enzymatic digestions, manual and automatic Edman degradations, and mass spectrometry. It is a 72 residue peptide (molecular mass 8388 Da), with six cysteines forming three disulfide bridges connecting residues 7-43, 23-39, and 26-52, with blocked N- and C-termini, and lacking the amino acids histidine, methionine, and tryptophan. The CHH-I of Procambarus bouvieri is compared with the other known CHHs from Orconectes limosus (98.6% identity), Homarus americanus isomorph A (83.3% identity), Homarus americanus isomorph B (79.2% identity), and Carcinus maenas (61.1% identity).

Bovine alpha 2-antiplasmin. N-terminal and reactive site sequence

Bovine alpha 2-antiplasmin (alpha 2AP) has been purified and partially characterized. The amino acid composition is very similar to that of human alpha 2AP, and the N-terminal (23 residues determined) and reactive site loop sequences (42 residues determined) are highly homologous to those of the human protein. Compared with human alpha 2AP, bovine alpha 2AP has an 18-residue N-terminal extension, homologous with part of the pre-sequence of human alpha 2AP. A re-investigation of the N-terminal sequence of freshly prepared human alpha 2AP reveals a new form extended by 12 residues.

Amino acid composition and immunochemical properties of AcPase III and AcPase IV representing glycoforms of the lower molecular weight, tartrate-resistant acid phosphatase of the frog liver

1. Amino acid composition and immunological properties of the frog liver LMW AcPase forms: AcPase III and IV were examined. 2. AcPase III and IV show nearly identical amino acid composition and close immunological similarity. 3. These results indicate protein identity of both the enzyme forms and together with our previous data [Kubicz A., Szalewicz A. and Chrambach A., Int. J. Biochem. 23, 413-419 (1991)] demonstrate that generation of AcPase III and IV is a modification of the same enzyme protein by glycosylation processes. 4. Differences in immunoreactivity between AcPase III and IV were observed and discussed to be due to their altered conformations.

Separation of porcine pepsinogen A and progastricsin. Sequencing of the first 73 amino acid residues in progastricsin

Porcine pepsinogen A (EC 3.4.23.1) and progastricsin (EC 3.4.23.3) have been separated by chromatography on DEAE-cellulose followed by chromatography on DEAE-Sepharose. Agar gel electrophoresis at pH 6.0 showed the presence of three components of pepsinogen A and two of progastricsin. During activation at pH 2 a segment of 43 amino acid residues (the prosegment peptide) is cleaved from the N-terminus of progastricsin. The sequence of this was determined; in addition, the first 30 residues of gastricsin were sequenced. The sequence of the first 73 amino acid residues of progastricsin shows an overall identity with progastricsins from man, monkey and rat of 67%. The overall identity with other zymogens for gastric proteinases is 27%. The highly conserved Lys36p (pig pepsinogen A numbering) is changed to Arg in porcine progastricsin.

Purification and characterisation of antigenic gliadins in coeliac disease

Two gliadins, known to be especially antigenic in coeliac disease, were purified to homogeneity by a series of ion-exchange chromatography steps. Their N-terminal amino acid sequences showed minor differences but clearly classified them as gamma-type gliadins. The purified gliadins were further characterised with respect to amino acid composition, molecular mass and E1(1%)cm at 276 nm. Based on these properties it is suggested that one of them is identical to a gamma-type gliadin, earlier characterised by its nucleotide sequence, whereas the other has not previously been described. The purification procedure may form the basis for the development of a more differentiated analysis of circulating antibodies for diagnosis and makes clinical testing of the toxicity of defined gliadin peptides feasible.

Comparison of structure and activities of peroxidases from Coprinus cinereus, Coprinus macrorhizus and Arthromyces ramosus

Initial structural and kinetic data suggested that peroxidases from Coprinus cinereus, Coprinus macrorhizus and Arthromyces ramosus were similar. Therefore they were characterized more fully. The three peroxidases were purified to RZ 2.5 and showed immunochemical identity as well as an identical M(r) of 38,000, pI about 3.5 and similar amino acid compositions. The N-termini were blocked for amino acid sequencing. The peroxidases had similar retention volumes by anion-exchange and gel-filtration chromatography. All peroxidases showed multiple peaks by Concanavalin A-Sepharose chromatography. The Concanavalin A-Sepharose profiles were different and depended furthermore on a fermentation batch. Tryptic peptide maps were very similar except for one peptide. This peptide contained an N-linked glycan composed of varying ratios of glucosamine and mannose for the three peroxidases. Rate constants and their pH dependence were the same for the three peroxidases using guaiacol or iodide as reducing substrates. We conclude that peroxidases from Coprinus cinereus, Coprinus macrorhizus and Arthromyces ramosus are most likely identical in their amino acid sequences, but deviate in glycosylation which, apparently, has no influence on the reaction rates of the enzyme. We suggest, that the Coprinus fungi express one peroxidase only in contrast to the lignin-degrading white-rot Basidiomycetes, which produce multiple peroxidase isozymes.

Group V allergens in grass pollens: IV. Similarities in amino acid compositions and NH2-terminal sequences of the group V allergens from Lolium perenne, Poa pratensis and Dactylis glomerata

Monoclonal antibodies (PpV4) raised against Phleum pratense group V allergen were used for immuno-affinity chromatography of cross-reacting group V allergens from related grass species. Fractions enriched in group V allergen were obtained from Lolium perenne, Poa pratense and Dactylis glomerata extracts. The major components in these fractions were found in the Mwr range 25-28 kD. IgE binding to these components was shown using a pool of grass allergic sera, by SDS-PAGE immunoblotting. These fractions were electroblotted from tricine SDS-PAGE gels onto a polyvinylidene-difluoride membrane and selected group V bands were directly cut out and used for amino acid analysis and NH2-terminal sequencing. Both the amino acid compositions and the NH2-terminal sequences obtained for each group V allergen were almost similar to each other and to the sequence and composition of the previously described allergen Phl p V from Phleum pratense. A common trait of the investigated allergens, is the very high contents of alanine (25-32%) and the presence of the modified amino acid, hydroxyproline.

In situ alkylation of cysteine residues in a hydrophobic membrane protein immobilized on polyvinylidene difluoride membranes by electroblotting prior to microsequence and amino acid analysis

For identification of cysteine residues on microsequence analysis it is crucial to derivatize the sulfhydryl groups. This reaction requires a desalting step which often represents a major obstacle, especially if the sample consists of limited amounts of a hydrophobic membrane protein. An alkylation procedure is described, allowing efficient derivatization (greater than 90%) of cysteines and cystines even in low microgram quantities, as revealed by test analyses with lysozyme and a hydrophobic membrane protein. The modified protein is recovered in high yields in a form suitable for both microsequence analysis and amino acid analysis. The method involves electrophoretic desalting by miniaturized Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and in situ alkylation after electro-transfer onto polyvinylidene difluoride membranes. Precautions against NH2-terminal blocking during sample preparations are provided. The general applicability of the method is illustrated by the structural characterization of the low abundance membrane receptor for human urokinase plasminogen activator.

Comparison of different staining methods for polyvinylidene difluoride membranes

Several new staining methods for polyvinylidene difluoride membranes, including mercurochrome, silver and dimethylaminoazobenzene isothiocyanate staining were compared with Coomassie Brilliant Blue and gold staining. Of these, Coomassie was most versatile and completely compatible with ensuing microsequencing, immunostaining or other visualization methods, while gold and silver staining were more sensitive. Mercurochrome allows selective detection of sulfhydryl-containing proteins while dimethylaminoazobenzene isothiocyanate staining may allow quantitation of sequenceable protein.

Determination of cysteine plus half-cystine in protein and peptide hydrolysates: use of dithiodiglycolic acid and phenylisothiocyanate derivatization

Cysteine and half-cystine in proteins and peptides can be determined by acid hydrolysis in the presence of dithiodiglycolic acid, derivatization with phenyl isothiocyanate, and HPLC separation of the phenylthiocarbamyl amino acids. The determination requires no additional sample handling, oxidation, reduction, alkylation, or desalting. Samples containing cystine are treated in the same manner as those containing cysteine. Derivatization of cysteine or half-cystine by dithiodiglycolic acid has no effect on any other amino acids. Recovery of the PTC-cysteine derivative is greater than 90% over the linear range of 5 pmol to 1 nmol. Precision of the cysteine plus half-cystine determination is equivalent to that observed for all other amino acids. Structure work on the derivative indicates that it is a mixed disulfide containing cysteine and thioglycolic acid.

Characterization of the major allergen of Cynodon dactylon (Bermuda grass) pollen, Cyn d I

An allergen from Cynodon dactylon (Bermuda grass) pollen, Cyn d I, has been purified by a combination of concanavalin A-Sepharose affinity chromatography, and carboxymethyl-Sepharose chromatography. The allergen constitutes the major allergenic component of the pollen extract as observed by immunoelectrophoretic techniques, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, an IgE-inhibition experiment, and skin testing. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Cyn d I is presented as a dominant 32 kd band and a minor 29 kd band, both binding IgE. Both bands are identified by monospecific rabbit antibodies (Abs) raised against Cyn d I. These Abs only weakly precipitate allergens from other grass species, indicating that Cyn d I possesses some unique immunochemical properties. Two of four purified murine monoclonal Abs raised against Cyn d I also bind to both bands of Cyn d I, indicating that the bands represent isoallergens with slightly different immunochemical properties. All four monoclonal Abs cross-react with pollen components from other grass species, especially Poa pratensis and Dactylis glomerata. The NH2-terminal sequence corresponding to approximately 10% of the complete sequence was determined, and it revealed high homology to the corresponding sequence of the major allergen of Lolium perenne, Lol p I. From the amino acid composition determination and immunoelectrophoretic comparison, the amount of Cyn d I in the source whole-pollen extract was estimated to be 15% wt/wt.

The NH2-terminal amino acid sequence of the immunochemically partial identical major allergens of Alder (Alnus glutinosa) Aln g I, birch (Betula verrucosa) Bet v I, hornbeam (Carpinus betulus) Car b I and oak (Quercus alba) Que a I pollens

The tree pollen major allergens (Aln g I), Bet v I, Car b I and Que a I, were purified to near homogeneity. Rabbit antibodies raised towards the major allergen Bet v I react with the major allergens of alder, hazel, hornbeam and oak, although with distinct variation in affinity. Immunochemically the major allergens seem to resemble one another more within than between the botanically established families of the fagale order. The physico-chemical parameters (molecular weight, pI values, amino acid composition and NH2-terminal amino acid sequence) of the major allergens exhibit a higher degree of consistency than do the immunochemical parameters, indicating that nuances in the allergens' secondary and tertiary structures are likely to govern the immunochemical differences.

Group V allergens in grass pollens. I. Purification and characterization of the group V allergen from Phleum pratense pollen, Phl p V

An allergen from Phleum pratense (timothy) pollen, Phl p V, has been isolated by a combination of copper chelate affinity chromatography and ion exchange chromatography. Phl p V binds IgE from serum of grass-sensitized donors as revealed in immunoelectrophoretic techniques and in SDS-PAGE immunoblot, and luminescence immunoassay (LIA) inhibition experiments indicate that the allergen represents a significant part of the IgE binding capacity of the extract. In immunoelectrophoresis, Phl p V is revealed as a single precipitate. However, molecular weight studies show that Phl p V consists of at least two isoforms with similar immunochemical properties, but with different molecular size. After SDS-PAGE treatment purified Phl p V is identified as two IgE-binding components, Phl p Va and Phl p Vb, with molecular weights 33 and 29 kD. After HPLC gel filtration, Phl p Va and Phl p Vb are identified in the major 30-kD eluate. After Sephadex G75 gel filtration of whole pollen extract, Phl p V is identified in fractions corresponding to molecular weights 47 and 25 kD. The 47-kD fraction corresponds to Phl p Va/Phl p Vb as seen in SDS-PAGE, while the 25-kD component presumably corresponds to a degradation product present in whole pollen extract. The NH2-terminal sequence of Phl p V, corresponding to approximately 10% of the molecule, has been determined. The sequence shows minor variations in some residues and contains besides many alanine residues also hydroxyproline; the sequence reveals no homologies to any known NH2 terminal sequence of other proteins. The amino acid composition, revealing 26 mole % alanine and no cysteine, does not show any similarities to other known amino acid compositions of allergens. From the amino acid composition determination and an immunoelectrophoretic comparison, Phl p V is estimated to represent 6% (w/w) of the whole pollen extract.

Purification and characterization of the major dog allergen, Can f I

An important dog-hair and dander-specific allergen Ag13 has been purified by means of immunoaffinity chromatography utilizing rabbit antibody specific for Ag13. Purity was judged to be very high as detected by crossed immunoelectrophoresis and SDS-PAGE. The purified allergen was subjected to amino acid analyses. Molecular weight was about 22 kD in HPLC-gel filtration and 25 kD in SDS-PAGE with an additional band at 18 kD. In vitro IgE binding of the allergen was investigated by luminescence immunoassay (LIA) inhibition. Removal of Ag13 from dog hair and dander extract (DHD) removed 50 +/- 1.5% of the IgE binding capacity. The purified allergen inhibited up to 56.5% of the IgE activity to DHD as measured with a pool of serum from dog-allergic patients. Out of 26 dog-allergic patients, 24 had a positive skin-prick test to the allergen. Out of 23 dog-allergic patients, 16 reacted with the allergen in IgE immunoblotting. We suggest that Ag13 be termed Can f I. The allergen will be a marker allergen for environmental dog hair and dander exposure.

Amino acid sequences and structures of chicken and turkey beta 2-microglobulin

The complete amino acid sequences of chicken and turkey beta 2-microglobulins have been determined by analyses of tryptic, V8-proteolytic and cyanogen bromide fragments, and by N-terminal sequencing. Mass spectrometric analysis of chicken beta 2-microglobulin supports the sequence-derived Mr of 11,048. The higher apparent Mr obtained for the avian beta 2-microglobulins as compared to human beta 2-microglobulin by SDS-PAGE is not understood. Chicken and turkey beta 2-microglobulin consist of 98 residues and deviate at seven positions: 60, 66, 74-76, 78 and 82. The chicken and turkey sequences are identical to human beta 2-microglobulin at 46 and 47 positions, respectively, and to bovine beta 2-microglobulin at 47 positions, i.e. there is about 47% identity between avian and mammalian beta 2-microglobulins. The known X-ray crystallographic structures of bovine beta 2-microglobulin and human HLA-A2 complex suggest that the seven chicken to turkey differences are exposed to solvent in the avian MHC class I complex. The key residues of beta 2-microglobulin involved in alpha chain contacts within the MHC class I molecule are highly conserved between chicken and man. This explains that heterologous human beta 2-microglobulin can substitute the chicken beta 2-microglobulin in exchange studies with B-F (chicken MHC class I molecule), and suggests that the MHC class I structure is conserved over long evolutionary distances.

Human red cell acid phosphatase: purification and properties of the A, B and C isozymes

Human red cell acid phosphatase isozymes encoded by three alleles (ACP1*A, ACPI*B and ACP1*C), each of which generates two isozymes, (f) and (s), were purified to homogeneity. The molecular mass of the six isozymes (Af, As, Bf, Bs, Cf and Cs) was estimated to be 17-18 kDa, the mass of the f isozymes probably being slightly higher than that of the s isozymes. It was indicated that the isozymes react with p-nitrophenyl phosphate in the mono anionic state, and that a group with a pKa value of about 6, which may be histidine, is of importance for the catalytic function of the s isozymes. Significant differences between the f and s isozymes were observed with respect to specific activity. Km (p-nitrophenyl phosphate), Ki (p-aminobenzylphosphonic acid), amino acid composition, stability in the presence of urea, thermal stability, retention time in size-exclusion chromatography of the native isozymes and migration in sodium dodecyl sulphate polyacrylamide gel electrophoresis, In contrast, identical or similar properties were observed for the three genetically different f isozymes, and the same was the case for the three s isozymes. It is suggested that the f and s isozymes serve different functions in the cell.

Determination of amino acid compositions and NH2-terminal sequences of peptides electroblotted onto PVDF membranes from tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis: application to peptide mapping of human complement component C3

The combination of high-resolution Tricine-Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (H. Schägger and G. von Jagow (1987) Anal. Biochem. 166, 368-379) and electroblotting onto polyvinylidene difluoride (PVDF) membranes represents a powerful technique for the isolation of small amounts of peptides and protein fragments (Mr 1000-20,000) in a suitable form for amino acid sequencing, directly on the blotting membrane. Conditions for electrophoresis and electroblotting were optimized with respect to high transfer yield and suitability for both amino acid analysis and sequence determination of stained PVDF-bound peptides. Transfer yields were 50-80%, amino acid compositions including Cys were correct, and picomole quantities were sequenced with initial and repetitive yields as high as those we normally obtain for peptides in solution. The method was used for peptide mapping of polymorphic forms of human complement component C3.