Analytical techniques for cell fractions. XXII. Two-dimensional analysis of serum and tissue proteins: multiple gradient-slab gel electrophoresis

Identification and partial characterization of two major proteins of Mr 47,000 synthesized by bovine retinal endothelial cells in culture

Biosynthetic experiments with cultured bovine retinal endothelial cells have identified a glycoprotein of Mr 47,000 (Gp47) as a major component secreted into the medium. Gp47 is a non-collagenous glycoprotein with a pI of 4.6-5.5, which does not bind to either gelatin-Sepharose or heparin-Sepharose but is retained by concanavalin A-Sepharose. The Mr of this species decreases to approx. 42,000 in the presence of tunicamycin, indicating that it contains asparagine-linked oligosaccharides. A second protein of Mr 47,000 (P47) is present in the cell layer/matrix of these cultured cells. The electrophoretic mobility of P47 remains unaltered when synthesized in the presence of tunicamycin. Peptide-mapping experiments using N-chlorosuccinimide and Staphylococcus aureus V8 proteinase demonstrate that Gp47 and P47 are distinct proteins, and are not related to colligin, a membrane-bound collagen-receptor protein of similar size, or to SPARC, a major secreted product of parietal endodermal cells and sparse cultures of aortic endothelial cells.

Antithrombin III Glasgow: a variant with increased heparin affinity and reduced ability to inactivate thrombin, associated with familial thrombosis

A functional antithrombin III (AT III) deficiency has been identified in two generations of a family with a high incidence of thrombosis. The deficiency presented as approximately 50% reduction in heparin cofactor activity compared to its antigen concentration. No abnormality was detected by crossed immunoelectrophoresis in the presence or absence of heparin. Plasma from the propositus was precipitated with dextran sulphate, applied to heparin-Sepharose and the AT III stepwise eluted with NaCl. The AT III had a reduced ability to inactivate thrombin, when this was monitored by substrate hydrolysis or by SDS polyacrylamide gel electrophoresis. Its mobility was normal by the latter technique using 10-20% gradient gels under reducing and non-reducing conditions. AT III from the patient was reapplied to heparin-Sepharose and eluted with a NaCl gradient. An active pool eluted in the same NaCl concentration range used to purify normal AT III, while predominantly inactive AT III eluted at higher NaCl concentrations. It is concluded that this variant, designated AT III Glasgow, has increased affinity for heparin but reduced ability to inactivate thrombin.

Two-dimensional gel electrophoresis of proteins

The high-resolution capacity of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) makes it an excellent tool for the analysis and characterisation of complex protein mixtures. The evolution of two-dimensional electrophoresis is briefly described. The various steps involved in 2-D PAGE, the identification and characterization of proteins separated by 2-D PAGE and the quantitative and qualitative analysis of 2-D patterns are discussed in detail and some new approaches are described. In the final section a brief outline of some of the biomedical applications of 2-D PAGE to screening of body fluids, genetic diseases, inborn errors of metabolism, cancer and neoplastic transformation are discussed.

Separation of protein hormones

The purpose of this review is to highlight modern techniques in HPLC and electrophoresis used for protein hormone separations. The advent of biotechnological methods for production of synthetic polypeptides and recombinant proteins will have a significant future impact on the types of therapeutics and metabolites that need to be monitored in the clinical laboratory. The protein hormone examples given in this work were selected because of the comprehensive body of separation science literature and not necessarily for their future importance in medicine. The intention was to present an array of general methods and techniques which may be useful to the clinical investigator for analysis of any protein hormone.

Modification of the rat sperm flagellar plasma membrane during maturation in the epididymis

Previously, we demonstrated that surface radiolabeling of rat epididymal spermatozoa by lactoperoxidase-catalyzed iodination reveals a major component with an apparent molecular weight of 26,000 to 28,000 daltons (26 kDa) on spermatozoa from the cauda but not the caput epididymidis. To characterize this surface component further, sperm surface constituents radiolabeled by lactoperoxidase-catalyzed iodination were separated by 2-D PAGE. The 26 kDa component was localized by autoradiography and appeared as the major labeled acidic spot on cauda spermatozoa, but neither a radiolabeled spot nor a corresponding stained spot was present on caput spermatozoa. The 26 kDa spot was excised from 2-D gels of plasma membranes from cauda spermatozoa and utilized for immunization. The monospecific antiserum stained a single band of 26 kDa on Western blots of SDS-PAGE-separated plasma membranes from cauda spermatozoa and in a 100,000 X g supernatant fluid of the luminal contents of the cauda epididymidis. Immunohistochemical staining of cauda spermatozoa revealed antigen exclusively on the flagellar domain; the antigen was not seen on caput spermatozoa but first appeared in spermatozoa from the proximal corpus epididymidis. Immunoelectron microscopy confirmed the 26 kDa component was localized to the external face of the flagellar plasma membrane. Immunohistochemical staining of caput spermatozoa incubated in vitro with cauda epididymal luminal fluid revealed the 26 kDa component specifically bound the flagellar domain of immature spermatozoa.

Copurification and characterization of deacetoxycephalosporin C synthetase/hydroxylase from Cephalosporium acremonium

Deacetoxycephalosporin C synthetase (expandase), which catalyzes ring expansion of penicillin N to deacetoxycephalosporin C (DAOC), has been stabilized in vitro and purified to near homogeneity from the industrially important fungus Cephalosporium acremonium. Throughout the purification, the expandase activity remained physically associated with and in a constant ratio of 7:1 to DAOC hydroxylase activity. The latter activity mediates hydroxylation of DAOC to deacetylcephalosporin C (DAC). The copurified expandase/hydroxylase appeared to be monomeric, with a molecular weight of 41,000 +/- 2,000 and an isoelectric point of 6.3 +/- 0.3. Both catalytic activities required alpha-ketoglutarate, Fe2+, and O2 and were stimulated by ascorbate, dithiothreitol, and ATP. The Fe2+ requirement was specific, and sulfhydryl groups in the purified protein were apparently essential for both ring expansion and hydroxylation. The kinetics and stoichiometry of DAOC/DAC formation from the expandase/hydroxylase-catalyzed reactions suggested that ring expansion of penicillin N preceded hydroxylation of DAOC.

Antithrombin III Northwick Park: demonstration of an inactive high MW complex with increased affinity for heparin

It has been shown previously that antithrombin III Northwick Park has reduced ability to inactivate thrombin and is characterized by an additional anodal component on crossed immunoelectrophoresis (Howarth et al, 1985). We have applied plasma from an affected family member to heparin-Sepharose and eluted the antithrombin III with a salt gradient. Evidence is presented that a variant component has slightly higher affinity for heparin than normal antithrombin III. Furthermore, this variant component is present in plasma as an approximately 120,000 MW inactive antithrombin III complex that can be reduced with dithiothreitol to MW approximately 60,000, indicating disulphide bridging. Using ion-exchange chromatography, the inactive complex has been isolated and shown to migrate in the same position as the anodal peak on crossed immunoelectrophoresis.

A non-competitive enzyme immunoassay of human alpha-lactalbumin in biological fluids and tissue extracts

A sandwich non-competitive enzyme immunoassay for the measurement of human alpha-lactalbumin in serum, milk, and tumour tissue cytosol was developed using affinity-purified polyclonal antibody adsorbed to solid phase. The detection limits of this procedure in tubes (macromethod) and in wells of microtitre plates (micromethod) are 50 pg and 25 pg/sample, respectively, which means 2.5 micrograms/l of serum at appropriate dilution. The micromethod enables a reduction of the volumes used in the reaction with equal sensitivity, accuracy and reproducibility. A comparison of alpha-lactalbumin concentrations in serum of healthy, pregnant, and lactating women determined by our method with those measured formerly by radioimmunoassays proved the specificity of our procedure.

Characterization of a cDNA defining a gene family encoding TM30p1, a human fibroblast tropomyosin

We have isolated a cDNA that contains the complete coding sequence of a 3.0 X 10(3) base human fibroblast mRNA together with a large part of its 3' untranslated sequence. The deduced protein sequence is very similar if not identical to the sequence of horse platelet tropomyosin, a 247 amino acid protein. In vitro translation of an SP6 transcript of this cDNA reveals that the protein product of the 3.0 X 10(3) base mRNA is TM30p1, one of the five proteins in human fibroblasts that have been shown to possess the physical and chemical characteristics of tropomyosin. This mRNA is encoded by a gene family that consists of a functional gene and multiple RNA-copy pseudogenes. This family of sequences is distinct from the gene family encoding TM30nm, a cytoskeletal tropomyosin very similar in electrophoretic mobility to TM30p1, but which shows significant differences in primary structure.

Identification and isolation of a variant surface glycoprotein from Trypanosoma vivax

The protozoan Trypanosoma vivax is one of the most important agents of African trypanosomiasis, a disease that hinders the productive use of livestock in one-third of the African continent. Trypanosoma vivax is also present in the Caribbean and in South America, posing a threat to the livestock industries of the tropical and subtropical world. Much less is known of the biology of this trypanosome than of the better studied T. brucei and T. congolense. One of the variant surface glycoproteins (VSGs) of a West African stock of T. vivax was identified, purified, and partially characterized by the use of a combination of highly resolving techniques to maximize information from the relatively small amount of parasite material available. The molecular weight of the isolated protein (46,000) is smaller than that of VSGs from other species. As with T. brucei VSGs the protein from T. vivax is complexed with sugars and incorporates 3H when living trypanosomes are incubated with [3H]myristic acid, but the T. vivax molecule is more hydrophobic than the T. brucei molecule. The small size of the T. vivax VSG may have a bearing on the functional and evolutionary relationships of variant antigens in trypanosomes.

Isolation by preparative isoelectric focusing of a direct acting fibrinolytic enzyme from the venom of Agkistrodon contortrix contortrix (southern copperhead)

Fibrolase, a blood clot-lysing enzyme, was isolated from the venom of the snake Agkistrodon contortrix contortrix using preparative scale isoelectric focusing in the recycling isoelectric focusing (RIEF) apparatus. Two sequential purifications, beginning with 1.0 g of whole, dried venom, were employed. A pH 6-8 range gradient effected the first separation. While 100% of the enzyme was recovered in three fractions, 43% (one fraction) had 70% purity. The second run was a refractionation of three, pooled fractions from the first run, in a 0.7 pH range gradient. Of the fibrolase in the venom, 63% was recovered in four fractions. One of these represented 29% of venom fibrolase, with 97% purity. Gel filtration chromatography removed most of the remaining, higher molecular weight contaminants of the RIEF-purified enzyme.

Implantation associated changes in uterine secreted proteins

Cross sectional segments were removed from the uteri of pregnant and pseudopregnant mice and incubated in vitro with labeled amino acids. Proteins that were synthesized and secreted by these explants were separated by two-dimensional polyacrylamide gel electrophoresis and localized by fluorography. As expected, the overall amount of labeled protein secreted into the medium was greater with tissue removed from implantation sites, or an artificially induced deciduoma, than it was with tissue from non-decidualized areas. It was not possible, by means of visual examination of the gels, to determine whether qualitative changes occurred in the patterns proteins that were released. However, by means of dual label ratios, it was demonstrated that the synthesis and secretion of individual proteins was regulated differentially. Furthermore, it was found that when the stimulus for decidualization was a normal implanting embryo, the pattern of protein enhancement was different than it was with an intrauterine thread. The finding that the uterus can distinguish between these two deciduogenic stimuli implies that unique signal factors, which may be important for the establishment of pregnancy, are released by the mouse embryo before implantation.

Characterization and fibre type distribution of a new myofibrillar protein of molecular weight 32 kDa

A new basic protein of molecular weight 32 kDa has been isolated and purified to homogeneity from skeletal muscles rich in type I fibres. By the use of a specific monoclonal antibody, the protein has been shown to be present in all type I fibres and some type II fibres, the number of which varies with the muscle and the region of the muscle sectioned. A protein of similar properties could not be isolated from rabbit muscles consisting predominantly of type II fibres. By fluorescence microscopy, the protein has been shown to be located in the Z-disc from which the presence of divalent cations, probably calcium, facilitates its extraction at low ionic strength. The protein is unusual in that its distribution does not correlate completely with the known muscle fibre types and in that as yet there is no evidence for the presence of an isoform in those cells that do not stain with the specific antibody for the 32 kDa protein isolated from slow muscles.

Basic proteins in the human aortic intima: nonequilibrium two-dimensional electrophoretic analysis of tissue extracts

The protein composition of atheroma-free human thoracic intima was compared with that containing fatty streaks or fibro-fatty lesions utilizing two-dimensional gel electrophoresis (2-DE) and silver staining. Intimal proteins extracted with 9 M urea were separated by nonequilibrium pH gradient electrophoresis (NEPHGE) followed by polyacrylamide gel electrophoresis (PAGE) in the second dimension. NEPHGE-PAGE of proteins extracted from atheroma-free intima revealed several major proteins: actin, tropomyosin-like proteins, proteins with relative molecular weight (Mr) of 250,000 (P250), two proteins with Mr about 15,000 (P15a, P15b), and many medium proteins such as a myosin heavy chain, two myosin light chains, and proteins P47, P44, P32, P27, P20a, P20b, P19a, P19b. Several additional proteins were observed in intimas with fatty streaks and fibro-fatty lesions. Most of them, such as albumin, transferrin, Apo A-I, alpha 1-antitrypsin, fibrinogen beta-chain, IgG, appear to originate from plasma. Differences in protein composition of intima with fibro-fatty streaks compared with adjacent lesion-free intima varied from case to case and need further study. NEPHGE-PAGE in combination with isoelectric focusing (ISO)-PAGE revealed more intimal proteins in atheroma-free and diseased aortas than either method alone, proteins which might be quantitated, isolated for binding studies, and further evaluated for their potential role in atherogenesis.

The mRNA and RNA-copy pseudogenes encoding TM30nm, a human cytoskeletal tropomyosin

We have determined the sequence of a 2.5 kb mRNA in human fibroblasts encoding a 248 amino acid cytoskeletal tropomyosin. The protein product of this mRNA is TM30nm, one of five tropomyosin-like proteins in human fibroblasts. The structural gene encoding this mRNA can also produce a 1.3 kb mRNA encoding a 285 amino acid skeletal muscle alpha-tropomyosin by tissue-specific alternative mRNA splicing. However, the multiple RNA-copy pseudogenes of this gene family are derived largely if not exclusively from transcripts processed according to the pattern observed in non-muscle cells.

Polymerization of intact beta 2-microglobulin in tissue causes amyloidosis in patients on chronic hemodialysis

Systemic amyloidosis with a predilection for bone and synovium may complicate the course of patients on long-term hemodialysis. This form of amyloidosis can be typed as distinct from other amyloid diseases by using small tissue samples obtained by bone biopsy and at postmortem. Immunoblot analysis of two-dimensional gels of partially solubilized amyloid fibrils established that tissue deposits are composed of monomers, dimers, and higher polymers of beta 2-microglobulin (beta 2m) and that amyloid P component was also present. Anti-beta 2m antiserum recognized fibrils, as shown by immunoelectron microscopy. Purified monomer isolated from dissociated fibrils yielded peptides corresponding to the entire known sequence of beta 2m. Virtually all serum beta 2m, as well as that present in tissue fluid bathing amyloid fibrils, was monomeric. Hemodialysis-related amyloidosis is an example of a deposition disease occurring in hemodialysis patients. We have shown conclusively that, in this amyloid disease, polymerization of an intact normal serum protein to a fibrillar configuration may occur without proteolysis. We propose the designation A beta 2m for this form of amyloid fibril subunit protein.

Isolation of undegraded free and membrane-bound polysomal mRNA from rat brain

A new procedure is described for the isolation of undegraded free and membrane-bound polysomal mRNA from rat brain in which polysomes are simultaneously separated from soluble components of the cell and slowly sedimenting ribosome species and concentrated by rate-zonal centrifugation on short linear sucrose gradients. This avoids the problem encountered in conventional procedures of pelleting polysomes along with membranous materials that are not solubilized by detergents and that appear to contain traces of nucleases. It also permits a more thorough analysis of the mRNA populations actively engaged in protein synthesis, since both polyadenylated and nonpolyadenylated mRNAs are isolated together. Moreover, the likelihood of sedimenting nonpolysomal mRNP particles along with polysomes is reduced by using rate-zonal rather than pelleting centrifugation. The translational activity in vitro of free and membrane-bound polysomal RNA prepared in this way is high and is about 1.5 times that of RNA prepared by a conventional pelleting technique. The difference is attributable to better preservation of large mRNAs, as inferred from two-dimensional gel electrophoretic analysis of translation product abundance. The recovery of both classes of polysomal RNA is about 90%. The method is simple, efficient, and adapted for isolation of small amounts of polysomal RNA.

Axokinin phosphorylation by cAMP-dependent protein kinase is sufficient for activation of sperm flagellar motility

Using a selective inhibitor of cAMP-dependent protein kinase, N-[2(methylamino)ethyl]-5-isoquinolinesulfonamide (H-8), the requirement for cAMP-dependent phosphoproteins in the initiation of dog sperm flagellar motility was examined. H-8 inhibited motility of live as well as reactivated sperm in a dose-dependent manner. The half-maximal inhibition of reactivated motility (32 microM) paralleled the inhibition of pure catalytic subunit of cAMP-dependent protein kinase (50 microM) measured under the same conditions. H-8 inhibited protein phosphorylation both in whole models and in isolated Nonidet P-40 (NP-40) extracts of sperm. Axokinin, the heat-stable NP-40-soluble protein whose phosphorylation is required for flagellar reactivation, represented 97% of the de novo phosphate incorporation in the NP-40 extract after stimulation by cAMP. 500 microM H-8 inhibited axokinin phosphorylation by 87%. When sperm were reactivated in the presence of up to 5 mM H-8 with NP-40 extract that had been prephosphorylated with cAMP-dependent protein kinase, then neither cAMP nor cAMP-dependent protein kinase activity was required for full flagellar reactivation. If sperm were rendered completely immotile by pretreatment with H-8, then the resulting model remained immotile in the continued presence of H-8 unless prephosphorylated axokinin was added. These results suggest that phosphorylated axokinin is not only required for flagellar reactivation but is sufficient as well.

Silver staining of proteins: standardized procedure for two-dimensional gels bound to polyester sheets

A system for the simultaneous silver staining of numerous two-dimensional gels bound to polyester sheets is proposed. Under controlled conditions, a very good reproducibility of staining can be obtained, even between different experiments. Procedures to avoid artifacts due to polyester sheets (background, silver mirror, and vertical streaking) are described.

A nonurea electrophoretic gel system for resolution of polypeptides of Mr 2000 to Mr 200,000

A sodium dodecyl sulfate-polyacrylamide gel electrophoresis system which resolves proteins and peptides from Mr 2000 to Mr 200,000 is described. Gradients of polyacrylamide, crosslinker, and glycerol buffered in Tris-phosphate (pH 6.8) are employed. Neither urea nor a stacking gel is required. This system has been used to separate molecules below Mr 3000 which differed by only seven amino acid residues, yet has the capacity to survey masses up to Mr 200,000 on the same gel. Examples are given for separations of myoglobin cyanogen bromide fragments and adrenocorticotropin peptides. Utilizing the same gradient slab gel system in tandem with isoelectric focusing, a two-dimensional separation pattern of mammalian liver cell lysate is shown. A comparison of two different silver stain methods with this system is also given.

Self and non-self discrimination by "restriction proteases"

I propose that an organism possesses a set of specific enzymes ("restriction proteases") that cleave self proteins at defined amino acid sequences unless these sequences are rendered inaccessible by glycosylation. Intracellular proteins are degraded by restriction proteases when cells die. In this way, intracellular proteins remain undetected by the immune system. I propose that some autoimmune diseases are caused by the absence of a specific restriction protease.

Ultrastructural morphology and protein content of the internal organic material of rat otoconia

Otoconia taken from the maculae of the saccule and utricle of the rat inner ear were investigated using transmission electron microscopy (TEM). Their ultrastructure was compared using various decalcification techniques. Similar preparations were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to assess their protein constituents. TEM results show loss of organic material during prolonged decalcification. This is not seen in samples decalcified overnight. The SDS-PAGE results show that rat otoconia contain a major broad band of 90-100 kDa, a major thin band of 56 kDa, and three other bands of 33, 45, and 50 kDa. The band of 56 kDa may be associated with the surface of the otoconia.

Biochemical characterization of chicken secretory component

Human dimeric IgA was injected i.v. into chickens whose bile was then collected. The human IgA which had been transported across the hepatocytes of the chicken was subsequently purified from the bile and shown to be associated with a protein of 80 kDa and pI 4.6, which reacted with rabbit antisera to chicken bile proteins but not with an antiserum to human alpha chain. The chicken bile protein thus has functional and biochemical properties similar to those of mammalian secretory component.

Increased binding to ADP-stimulated platelets and aggregation effect of the dysfibrinogen Oslo I as compared with normal fibrinogen

Interactions of the dysfibrinogen Oslo I with platelets were investigated. This fibrinogen is a B beta-chain variant with faster than normal fibrin monomer polymerization. Fibrinogen Oslo I acted more efficiently in ADP-induced platelet aggregation, and bound to gel-filtered platelets with a higher affinity constant than did normal fibrinogen. At all concentrations more fibrinogen molecules became bound per platelet with the dysfibrinogen than with normal fibrinogen, both when the fibrinogens were tested separately or as a mixture using 125I or 131I to label the two types. At high concentrations this was probably due to ligand polymerization of the dysfibrinogen. These observations indicate that the increased cofactor function in platelet aggregation may be related to the increased affinity of the dysfibrinogen for the platelets.

A statistical analysis of spot variation using the two-dimensional polyacrylamide gel electrophoresis

For the development of valid algorithms for matching protein spots between two-dimensional gels, it is essential that one has an understanding of the relative roles of the many sources of variability affecting the location of spots. We first consider the contribution of observers to the measurement variability of spot location, arriving at a simple model for these effects. Next we present an analysis of the variability in spot locations for a sample of gels containing duplicate gels for each sample. Our data indicate that both differences between duplicates and between samples are considerable, and that the size of the effects depends on the region of the gel being considered. In the discussion we examine several matching strategies that match large groups of gels based on algorithms which match two gels at a time.

Two-dimensional characterization of prostatic acid phosphatase, prostatic specific antigen and prostate binding protein in expressed prostatic fluid

Specimens of pooled prostatic fluid, collected by rectal massage from men under 50 years of age with no apparent prostatic disorders, were subjected to two-dimensional gel electrophoresis to study the composition of its proteins. In a preliminary study, a total of 57 major protein groups were detected. In the present study, we attempted to identify, in the two-dimensional gels, those that are related to prostate-associated proteins, i.e., prostatic acid phosphatase (PAP), prostatic specific antigen (PSA), and prostate binding protein (PBP). Individual proteins were recognized by the procedure of Western Blot using specific antisera with peroxidase-antiperoxidase as the staining reagent. Each protein spot in the two-dimensional gel was expressed, along the abscissa, by its isoelectric point (pI) and, along the ordinate, by the molecular weight (MW). PAP consisted of a train of more than ten protein spots that occupied an area in the gel from pI 7.0, MW 45,000 to pI 6.0, MW 50,000. Four protein spots with a MW of 34,000 and a pI range of 8.2-8.8 were identified as PSA. PBP was observed as having three protein spots that were located at pI 5.6-6.6 with a single MW of 15,000. For PAP and PSA, additional protein spots with lower MWs also stained positively with the specific antisera, suggestive of the presence of degradative products of these proteins. Following the removal of the serum-related proteins by an extensive absorption with anti-human serum antibody by affinity chromatography, the prostatic fluid contained 27 major groups of non-serum proteins. These non-serum proteins in the prostatic fluid included PAP, PSA, PBP, and their related smaller molecular species. These results indicate that the prostatic fluid contains PAP, PSA, PBP and that their presence and the patterns of their distribution in the two-dimensional gels should be considered as the characteristic property of the prostatic secretions.

Sequence homology analysis of proteins by chemical cleavages: using a mono and two dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis

The examination of possible sequence homology in proteins using SDS-PAGE systems after chemical cleavage is described. After SDS-PAGE, the establishment of amino acid compositions, the techniques of staining gel and five different methods of chemical cleavages (cyanogen bromide, BNPS-skatole, hydroxylamine, formic acid and nitrothiocyano benzoic acid) have been used for peptide mapping studies. Potential applications of this technique are discussed from both the biochemical and immunochemical point of view.

Equilibrium denaturation of pituitary- and recombinant-derived bovine growth hormone

Holladay and co-workers [Holladay, L. A., Hammonds, R. G., & Puett, D. (1974) Biochemistry 13, 1653-1661] reported the presence of an equilibrium intermediate in the guanidine hydrochloride (GdnHCl) induced denaturation of pituitary-derived bovine growth hormone (p-bGH). Since then, numerous reports have appeared demonstrating the inherent heterogeneity in p-bGH. In this report we show that a standard preparation of p-bGH can be separated into two components of almost equal abundance differing in molecular weight by approximately 1000. Each of these two components could give rise to different denaturation transitions which would be interpreted as evidence for equilibrium intermediates. We report here the equilibrium denaturation of bGH produced by Escherichia coli through recombinant DNA technology. The recombinant-derived bGH (r-bGH) is more homogeneous than that derived from pituitary sources and is greater than 95% a single polypeptide entity. Nevertheless, the GdnHCl-induced denaturation profiles of both recombinant bGH and pituitary bGH are very similar. The presence of equilibrium intermediates is verified by the asymmetry of the denaturation transition as measured by size-exclusion high-performance liquid chromatography and by noncoincidence of the denaturation transitions as observed by ultraviolet absorbance, fluorescence intensity, and circular dichroism. These findings conclusively show that the secondary structure of bovine growth hormone is more stable than the tertiary structure and is consistent with a framework model of protein folding.

Effect of aging on human aortic protein composition. II. Two-dimensional polyacrylamide gel electrophoretic analysis

Arterial intima proteins were extracted by 9 M urea from matching histologically atheroma-free areas of 27 human thoracic aortas of both sexes from younger (15-34) and older (35-82) age groups and studied after separation by high-resolution two-dimensional polyacrylamide gel electrophoresis. Seventeen specific protein groups on each gel were identified according to their relative charges and molecular weights and their distribution in the two age groups compared. Some plasma-derived proteins occurred rarely in young aortas while they were consistently found in those from older cases, i.e., protein group 4 (alpha 1-antichymotrypsin) 1/13 (8%) vs 12/14 (86%), group 7 (haptoglobin beta-chain) 1/13 (8%) vs 13/14 (93%) and groups 6 and 9 (IgG chains) 3/13 (23%) vs 9/14 (64%), respectively. Other plasma-derived proteins such as group 3 (albumin) and 5 (alpha 1-antitrypsin) were identified in all samples of both age groups but their expression in the aortic intima increased with age. Proteins which are typically found intracellularly such as those from groups 11 (actin), 12 (cytoskeleton proteins), and 13 (tropomyosin-like proteins) appeared in samples of intima of both age groups but were less apparent in older specimens. These studies suggest that the changes in aortic intima protein distribution in the absence of atherosclerosis closely correlate with histological changes such as intimal thickening often found with aging, providing new sensitive markers of vascular senescence.

Chromosomal localization of structural genes and regulators in wheat by 2D electrophoresis of ditelosomic lines

Among the 782 spots observed in two-dimensional gel electrophoresis of denatured proteins from etiolated wheat shoots, 185 were found to be variable between the euploid and 26 ditelosomic lines of 'Chinese Spring'. Thirty-five structural genes were located on 17 chromosome arms. Numerous intensity changes showing alterations in protein levels were observed and led to the following statements: 1) regulators are frequently found and can be assigned for a same polypeptide to various chromosome arms; 2) for most polypeptides homoeologous arms do not manifest similar effects; 3) nevertheless, when affecting the same polypeptide, homoeologous arms display in most cases identical regulatory effects; 4) gene dosage compensation is observed in only one out of four homoeoallelic situations.

Selective overproduction of human dihydrofolate reductase in a methotrexate-resistant human-mouse somatic cell hybrid

The development of methotrexate (MTX) resistance in cultured cells results in increased levels of the drug's target enzyme dihydrofolate reductase (DHFR). Stepwise-selected MTX-resistant sublines originating from an MTX-sensitive human-mouse hybrid expressed elevated DHFR levels and human-DHFR specific gene sequence amplification. By high resolution two-dimensional polyacrylamide gradient electrophoresis, human DHFR was shown to be selectively overproduced in VB2a-100 MTX-resistant cells whereas mouse DHFR protein "spots" present in MTX-sensitive parental hybrid were absent in these cells exhibiting 100 microM MTX resistance. These findings and those in a parallel study indicate that concurrent with overproduction of human DHFR and amplification DHFR sequences in VB2a-100, a loss of mouse-specific DHFR gene sequences occurred.

Heterogeneity of human skeletal muscle tropomyosin

Six polypeptides resolved by two-dimensional electrophoresis of homogenates from human skeletal muscle have been identified as tropomyosin by electrophoretic and immunochemical methods. The 6 proteins are consistently present in approximately the same abundance in normal biceps, deltoid, gastrocnemius, and quadriceps muscle. Analysis of samples from individuals with Becker's dystrophy, Duchenne dystrophy, limb girdle dystrophy, polymyositis, myopathy related to vitamin E deficiency, type II fiber deficiency, and from an infant with indistinct fiber type differentiation, however, showed quantitative variations in the tropomyosin pattern. Muscle with histochemically demonstrated type II fiber deficiency lacked two of the normal tropomyosin proteins and the type II myosin light chains. Muscles lacking type I myosin light chains were deficient in a different pair of tropomyosin proteins. The results suggest that normal human skeletal muscle contains one major type of tropomyosin protein (beta-tropomyosin) common to both fast and slow fibers, together with two other major proteins (alpha-tropomyosin and alpha'-tropomyosin), one of which is specific to fast fibers and the other to slow fibers. Preliminary data from the reaction of muscle homogenates with alkaline phosphatase indicate that 3 of the 6 tropomyosin polypeptides resolved by two-dimensional electrophoresis are phosphorylated forms of the alpha-, alpha'-, and beta-tropomyosins.

Subtyping of haptoglobin--presentation of a new method

A method is described for large scale routine phenotyping of haptoglobin (Hp) which allows complete subtyping without prior purification of the Hp molecule. The procedure includes polyacrylamide gel isoelectric focusing of reduced, neuraminidase treated serum or plasma samples, and nitrocellulose blots developed with the immunoperoxidase technique. Different variables including sample treatment, electrofocusing, blotting procedures, and immunoperoxidase visualization are discussed. Characteristic alpha-chain patterns allow identification of the common allotypes 2FS, 2SS, 2FF, IS, IF, and Johnson. Isoelectric variations in the beta-chain may also be recognized. For comparison, two-dimensional Hp-patterns are presented. The results from concurrent typing of 600 samples by ordinary starch gel electrophoresis and by the described isofocusing technique, are evaluated.

Two different variants of the same tropomyosin polypeptide in clones from GM1386 human skin fibroblasts

A new protein observed in two-dimensional electrophoresis patterns of proteins from the human skin fibroblast line GM1386 has been identified as a charge and molecular-weight variant of the type of tropomyosin found in smooth muscle (Tm:3). This is the second variant of Tm:3 found in GM1386 and represents a second site mutation in one of the genes coding for Tm:3.