Electrophoresis buffers for polyacrylamide gels at various pH

The effects of hydrostatic pressure on the conformation of plasminogen

Plasminogen undergoes a large conformational change when it binds 6-aminohexanoate. Using ultraviolet absorption spectroscopy and native PAGE, we show that hydrostatic pressure brings about the same conformational change. The volume change for this conformational change is -33 mL.mol-1. Binding of ligand and hydrostatic pressure both cause the protein to open up to expose surfaces that had previously been buried in the interior.

Molecular analysis of the cytolytic protein ClyA (SheA) from Escherichia coli

Escherichia coli K-12 carries a gene for a protein denoted ClyA or SheA that can mediate a cytolytic phenotype. The ClyA protein is not expressed at detectable levels in most strains of E. coli, but overproduction suitable for purification was accomplished by cloning the structural gene in an hns mutant strain. Highly purified ClyA protein was cytotoxic to macrophage cells in culture and caused detachment and lysis of the mammalian cells. Results from osmotic protection assays were consistent with the suggestion that the protein formed pores with a diameter of up to 3 nm. Using Acholeplasma laidlawii cells and multilamellar liposomes, we studied the effect of ClyA on membranes with varying compositions and in the presence of different ions. ClyA induced cytolytic release of the fluorescent tracer from carboxyfluorescein-loaded liposomes, and the release was stimulated if cholesterol was present in the membranes whereas addition of calcium had no effect. Pretreatment of the ClyA protein with cholesterol inhibited the pore formation, suggesting that ClyA could bind to cholesterol. Efficient coprecipitation of ClyA with either cholesterol or 1,2,3-trioctadecanoylglycerol in aqueous solutions showed that ClyA directly interacted with the hydrophobic molecular aggregates. We tested the possible functional importance of selected ClyA protein regions by site-directed mutagenesis. Defined mutants of ClyA were obtained with alterations in postulated transmembrane structures in the central part and in a postulated membrane-targeting domain in the C-terminal part. Our results were consistent with the suggestion that particular amphiphilic segments are required for ClyA activity. We propose that these domains are necessary for ClyA to form pores.

TrfA dimers play a role in copy-number control of RK2 replication

Copy-number regulation of the broad-host-range plasmid RK2 is dependent on the plasmid-encoded initiator protein, TrfA, and the RK2 origin of replication. The handcuffing model for copy-number control proposes that TrfA-bound oris reversibly couple to prevent the further initiation of plasmid replication when the copy number in vivo is at or above the replicon-specific copy number. TrfA mutants have been isolated which allow for oriV replication at elevated copy numbers. To better understand the mechanism of 'handcuffing', the copy-up TrfA(G254D/S267L) mutant was characterized further. In the present study we show by size exclusion chromatography and native gel electrophoresis that unlike wt TrfA which is largely dimeric, purified His6-TrfA(G254D/S267L) is primarily monomeric. In vivo, TrfA33(G254D/S267L) supports replication of an RK2 ori plasmid in trans at a greatly elevated copy number, while in cis the plasmid exhibits runaway replication. However, expression of either of two previously isolated DNA-binding defective TrfA mutants, TrfA33(P151S) or TrfA33(S257F), in a cell transformed with a mini-RK2 replicon encoding TrfA33(G254D/S267L) results in suppression of the runaway phenotype. His6-TrfA(P151S) and His6-TrfA(S257F) purify as dimers, and when expressed in vivo are incapable of supporting RK2 plasmid replication. In contrast, combination of the trfA(P151S) or trfA(S257F) mutation with the trfA(G254D/S267L) mutations results in the expression of mutant TrfA proteins which are mainly monomers and which can no longer restore copy control to replication directed by TrfA33(G254D/S267L) in vivo. On the basis of these findings a handcuffing model is proposed, whereby oriV-bound TrfA monomers are coupled by dimeric TrfA molecules.

An electrophoretic study on interactions of albumins of different species with immobilized Cibacron Blue F3G A

Albumins of different species, varying in electrophoretic mobility, were compared in their interaction with the dye Cibacron Blue F3G A. Immobilized by coupling to a high molecular weight dextran ("blue dextran"), the dye was used as a ligand in affinity electrophoresis in different setups. One-dimensional electrophoresis with blue dextran entrapped in an intermediate gel and two-dimensional applications with transverse gradients (affinity titration curves, zonal electrophoresis in linear ligand gradients) were performed. Compared to the human homologue, animal albumins albumins display more complex patterns and interaction profiles, depending on pH and ionic strength of the buffers. Results may differ considerably from those obtained by affinity chromatography, illustrating the additional screening potential of the electrophoretic methods. Comparison of different samples under the influence of ligand competition, reducing conditions, or denaturing agents gives supplementary information on conformational behavior of the proteins.

Transcytosis of alpha1-acidic glycoprotein in the continuous microvascular endothelium

By using perfusions and bolus administration, coupled with postembedding immunocytochemical procedures, we have identified the structures involved in the transport of derivatized orosomucoid (alpha1-acidic glycoprotein) across the continuous microvascular endothelium of the murine myocardium. Our findings indicate that: (i) monomeric orosomucoid binds to the luminal surface of the endothelium; (ii) it is restricted to caveolae during its transport across the endothelium; (iii) it is detected in the perivascular spaces at early time points (by 1 min) and in larger quantities at later time points (>5 min) from the beginning of its perfusion or its intravascular administration; (iv) no orosomucoid molecules are found in the intercellular junctions or at the abluminal exits of interendothelial spaces; and (v) the vesicular transport of orosomucoid is strongly inhibited by N-ethylmaleimide (>80%). Because, by size and shape, the orosomucoid qualifies as a preferential probe for the postulated small pore system, our results are discussed in relation to the pore theory of capillary permeability.

CooB plays a chaperone-like role for the proteins involved in formation of CS1 pili of enterotoxigenic Escherichia coli

CS1 pili serve as the prototype of a class of filamentous appendages found on the surface of strains of enterotoxigenic Escherichia coli. The four genes needed to synthesize functional CS1 pili in E. coli K12 are: cooA, which encodes the major pilin protein; cooD, which encodes a minor pilin protein found at the tip of the structure; cooC, which encodes a protein found in the outer membrane of piliated bacteria; and cooB. We show here that CooB, which is required for pilus assembly but is not part of the final structure, stabilizes CooA, CooC, and CooD. We previously reported that CooB is complexed with CooA in the periplasm and show here that CooB also is found complexed with CooD in the periplasm. CooB is associated with the membrane fraction only in the presence of CooC, suggesting that these two proteins also interact. This suggests that although it has no homology to known chaperone proteins, CooB serves a chaperone-like role for assembly of CS1.

DNA binding specificity of MunI restriction endonuclease is controlled by pH and calcium ions: involvement of active site carboxylate residues

Gel shift analysis reveals [Lagunavicius, A., & Siksnys, V. (1997) Biochemistry 36 (preceding paper in this issue)] that at pH 8.3 in the absence of Mg2+, MunI restriction endonuclease exhibits little DNA binding specificity, as compared with the D83A and E98A mutants of MunI. This suggests that charged carboxylate residue(s) influence the DNA binding specificity of MunI. In our efforts to establish the determinants of MunI binding specificity, we investigated the possible role of the ionic milieu, and we found that lowering pH or elevating Ca2+ levels per se induces specific DNA recognition by WT MunI. In contrast to the binding experiments at pH 8.3, gel shift analysis at pH 6.5 indicated tight sequence-specific binding of WT MunI in the absence of Mg2+, suggesting that protonation of active site carboxylate residue(s) which manifest anomalously high pKa value(s) control binding specificity. Interestingly, Ca2+ ion concentrations, which did not support DNA cleavage by MunI also induced DNA binding specificity in WT MunI at pH 8.3. To explore possible structural changes upon DNA binding, we then used a limited proteolysis technique. Trypsin cleavage of MunI-DNA complexes indicated that in the presence of cognate DNA the MunI restriction endonuclease became resistant to proteolytic cleavage, suggesting that binding of specific DNA induced a structural change. CD measurements confirmed this observation, suggesting minor secondary structural differences between complexes of MunI with cognate and noncognate DNA. These results therefore suggest that binding of MunI to its recognition sequence triggers a conformational transition that correctly juxtaposes active site carboxylate residues, which then chelate Mg2+ ions. In the absence of Mg2+ ions, at pH 8.3, conditions in which carboxylate groups would be expected to be completely ionized, electrostatic repulsion between charged carboxylates and phosphate oxygens is enhanced such as to interfere with specific DNA binding. Elimination of such repulsive constraints by replacement of carboxylate residues, by lowering pH, or by metal ion binding, then promotes MunI binding specificity.

Construction and overexpression of a synthetic gene for human DNA methylguanine methyltransferase: renaturation and rapid purification of the protein

A synthetic gene was constructed that encodes human DNA methylguanine methyltransferase (hMGMT). The synthetic gene was designed with a number of unique restriction sites to facilitate cassette mutagenesis and to reflect the preferences found among genes in Escherichia coli. Both the full-length gene and a gene for a functional variant (hMGMT delta C) that lacks the C-terminal 28 codons were constructed, and the genes were overexpressed using a T7 RNA polymerase promoter. The proteins are made in the form of insoluble aggregates but the truncated form of the protein (hMGMT delta C) has been successfully denatured, renatured, and purified to near homogeneity by ion exchange. Methyltransferase activity assays of hMGMT delta C demonstrate that the reconstituted protein has substantial DNA repair activity, though somewhat less than full-length hMGMT that had been expressed and purified in a soluble form. Mass spectrometry of a mixture of proteolytic fragments confirmed the protein sequence and indicated no detectable oxidation of the active site cysteine. The protein was determined to be monomeric by gel filtration chromatography, and circular dichroism spectra for renatured hMGMT delta C and fully soluble hMGMT are consistent with the renatured protein preparation being fully folded. Refolded hMGMT delta C had a curious propensity to form large aggregates in a time-dependent manner when injected into a dynamic light scattering instrument; this aggregation behavior was not observed for hMGMT purified in a soluble form. Differences in susceptibility to aggregation may account for differences in methyltransfer activity. Yields of purified protein were approximately 5 mg/liter of culture.

The role of pH and membrane porosity in preparative electrophoresis

The Gradiflow is a preparative electrophoresis apparatus, allowing fractionation based on a combination of size and charge of proteins in their native (unreduced) form. The preparative fractionation of two proteins of similar size and isoelectric point is demonstrated using the Gradiflow. A separation membrane of appropriate pore size was chosen and then fractionation was "fine tuned" by selecting an appropriate buffer pH to accentuate charge differences between the proteins of interest. Complete separation of mg quantities of bovine serum albumin and ovalbumin was achieved within 40 min.

Kinetic and structural evidence for the identification of 11-hydroxythromboxane B2 dehydrogenase as cytosolic aldehyde dehydrogenase

We have recently purified 11-hydroxythromboxane B2 dehydrogenase from porcine kidney and identified it as cytosolic aldehyde dehydrogenase (EC 1.2.1.3) based on amino acid analysis and other protein characteristics. In the present paper we have studied the catalytic interaction of thromboxane B2 (TXB2) with different aldehyde substrates and a potent aldehyde dehydrogenase inhibitor, disulfiram. TXB2 was a competitive inhibitor of the aldehyde dehydrogenase reaction in assays with 3,4-dihydroxyphenylacetaldehyde, a high affinity substrate. The conversion of TXB2 to 11-dehydro-TXB2 was also inhibited by propanal and disulfiram. The protein characteristics of the enzyme have also been further studied. The native enzyme is a tetramer and has an isoelectric point of 7.0 which is comparable with that of cytosolic aldehyde dehydrogenases from other species. Taken together the present data further indicate that 11-hydroxythromboxane B2 dehydrogenase is identical with cytosolic aldehyde dehydrogenase and that substrates and inhibitors of aldehyde dehydrogenase interact with thromboxane metabolism in vitro.

Structural and functional characterization of DsbC, a protein involved in disulfide bond formation in Escherichia coli

DsbC is a soluble protein of the bacterial periplasm that was identified genetically as being involved in protein disulfide formation. The gene sequence was corrected to include an additional proline residue and was then consistent with the molecular weight of the purified protein. Gel filtration and subunit hybridization indicate that DsbC is a stable dimer of identical subunits. Each subunit has a -Cys-Gly-Tyr-Cys- segment that forms an unstable and reactive disulfide bond; only the first cysteine residue is accessible, similar to thioredoxin and DsbA. The other two cysteine residues of DsbC form a buried, structural disulfide bond. The reactivities and stabilities of the active site disulfide bond of DsbC have been characterized and compared to that of DsbA. Both are very unstable and can be transferred rapidly to reduced proteins and peptides, although they differ somewhat in their kinetic reactivities. The two active sites of the DsbC dimer appear to function independently. DsbC is much more active than DsbA in catalyzing protein disulfide rearrangements, and this may be its main function in vivo.

Human leucocyte glycosylasparaginase is an alpha/beta-heterodimer of 19 kDa alpha-subunit and 17 and 18 kDa beta-subunit

Human lysosomal glycosylasparaginase (AGA; EC 3.5.1.26) consists of two glycosylated subunits, alpha and beta. Treatment with 3% SDS at 45 degrees C as part of a new purification scheme did not affect enzyme activity, but the alpha-subunit migrated an apparent 19 kDa peptide on SDS/PAGE instead of as a 24 kDa peptide, as observed without this SDS treatment. The N-terminal sequence was similar to that of the 24 kDa form, and, after reversed-phase h.p.l.c., the 19 kDa form was transformed to an apparent 24 kDa peptide on SDS/PAGE, indicating that their primary structures were identical. As the molecular mass of the alpha-subunit deduced from its cDNA was 19.5 kDa, the variation might be due to incomplete SDS coating of the 24 kDa form. This was confirmed by the tendency of the 24 kDa variant to polymerize even in the presence of SDS. The molecular mass of the beta-subunit was 17 and 18 kDa in accordance with previous reports. Chemical cross-linking with 1-ethyl-3-(3-dimethylaminopropyl)carbodi-imide resulted in the appearance of a 38 kDa peptide on SDS/PAGE which reacted with both the subunit-specific antisera on Western-blot analysis. On SDS/PAGE at pH 10.2 the active enzyme migrated as an apparent 43 kDa peptide. These results indicate that native human glycosylasparaginase is a heterodimer.

Antifibrinolytic activities of alpha-N-acetyl-L-lysine methyl ester, epsilon-aminocaproic acid, and tranexamic acid. Importance of kringle interactions and active site inhibition

alpha-N-acetyl-L-lysine methyl ester (NALME) is a lysine analogue that reportedly binds to low-affinity lysine binding sites in plasmin(ogen) and miniplasmin(ogen). In the studies presented here, we show that NALME has antifibrinolytic activity; however, unlike the therapeutic agents epsilon-amino-n-caproic acid (epsilon ACA) and tranexamic acid (TEA), the activity of NALME is based on inhibition of the plasmin active site. NALME (0.1-10 mM) significantly inhibited the amidase activity of plasmin, miniplasmin, and streptokinase-plasmin complex without affecting alpha-thrombin or tissue plasminogen activator. epsilon ACA and TEA (0.1-10 mM) did not affect the amidase activity of plasmin or miniplasmin. A kinetic analysis showed that NALME is a competitive inhibitor of D-Val-L-Lys-p-nitroanilide HCl (S-2251) hydrolysis by plasmin; NALME binding to plasmin completely prevented S-2251 binding. The Kl for the plasmin-NALME interaction was 0.4 mM. epsilon ACA and TEA inhibited fibrin monomer digestion by plasmin and miniplasmin without binding to the active site of either enzyme. This result suggests that epsilon ACA and TEA function as antifibrinolytics by disrupting the noncovalent association of fibrin monomer with a domain common to both plasmin and miniplasmin (probably kringle 5). NALME inhibited fibrin monomer digestion principally by decreasing amidase activity. NALME was the only lysine analogue that prevented fragment X formation; TEA and epsilon ACA primarily inhibited the formation of fragments Y and D. When plasmin was incubated simultaneously with alpha 2-antiplasmin and alpha 2-macroglobulin, epsilon ACA increased the fraction of plasmin reacting with alpha 2-macroglobulin; NALME had no effect on the plasmin distribution.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of transforming growth factor-beta 1 to methylamine-modified alpha 2-macroglobulin and to binary and ternary alpha 2-macroglobulin-proteinase complexes

The binding of 125I-labelled transforming growth factor-beta 1 (TGF-beta 1) to human alpha 2-macroglobulin (alpha 2M) was studied by native PAGE and autoradiography. TGF-beta 1 bound preferentially to alpha 2M-methylamine and minimally, if at all, to native alpha 2M. Preparations of alpha 2M-proteinase complex were generated by incubating a standard concentration of alpha 2M (0.4 microM) with different concentrations of trypsin, chymotrypsin or neutrophil elastase (0.04-2.0 microM). The 125I-TGF-beta 1-binding activity depended on the initial ratio of active proteinase to alpha 2M, or r value, used to form the alpha 2M-proteinase complex. With all three proteinases, r values of 2 or greater yielded preparations with unchanged or decreased TGF-beta 1-binding activity relative to native alpha 2M. By contrast, r values near 1 yielded preparations with significantly increased TGF-beta 1-binding activity. The results of [3H]thymidine-incorporation studies performed in mouse keratinocytes were consistent with the 125I-TGF-beta-binding experiments. alpha 2M-trypsin and alpha 2M-chymotrypsin prepared at an r value of 1.0 counteracted the activity of TGF-beta 1, whereas the equivalent complexes prepared at an r value of 3.0 had no effect. As determined by SDS/PAGE, 125I-TGF-beta 1 binding to alpha 2M-methylamine was at least 80% non-covalent. Reaction of alpha 2M-methylamine with iodoacetamide or 5,5'-dithiobis-(2-nitrobenzoic acid) decreased the percentage of covalent binding but had no effect on total binding. Neuraminidase treatment had no effect on the binding of 125I-TGF-beta 1 to alpha 2M-methylamine. Cleavage of the 'bait regions' in alpha 2M-methylamine by prolonged treatment with trypsin also had no effect. These studies suggest that TGF-beta 1 binding to alpha 2M is enhanced by conformational change in the proteinase inhibitor resulting from reaction with proteinase or amine. If both proteinase-binding sites in a single alpha 2M molecule are occupied, TGF-beta 1-binding activity is decreased or perhaps eliminated.

Binding of transforming growth factor-β1 to immobilized human α2-macroglobulin

Native alpha 2-macroglobulin (alpha 2M) and alpha 2M-methylamine were immobilized in 96-well microtiter plates. 125I-labeled transforming growth factor-beta 1 (TGF-beta 1) bound to both alpha 2M variants; however, greater binding was observed with alpha 2M-methylamine. Binding of 125I-TGF-beta 1 (0.2 nM) to immobilized alpha 2M-methylamine was inhibited by nonradiolabeled TGF-beta 1 (up to 74% with 0.4 microM TGF-beta 1). Approximately 10% of the TGF-beta 1-alpha 2M-methylamine complex was covalent. Treatment of alpha 2M-methylamine with iodoacetamide prior to immobilization completely eliminated covalent TGF-beta 1 binding; the total amount of 125I-TGF-beta 1-alpha 2M-methylamine complex detected was unchanged. The binding of 125I-TGF-beta 1 to immobilized alpha 2M-methylamine was not significantly inhibited by increasing the ionic strength to 1.0 M. Binding and complex dissociation were also unaffected by changes in pH within the range 6.9-8.9. Acidic pH dramatically decreased binding and promoted complex dissociation; no binding of 125I-TGF-beta 1 to immobilized alpha 2M-methylamine was detected at pH 3.5. The interaction of TGF-beta 1 with immobilized alpha 2M-methylamine was not significantly changed by 1.0 mM EDTA or 1.0 mM CaCl2. ZnCl2 (1.0 mM) completely eliminated binding. This result was not due to TGF-beta 1 precipitation or aggregation. Inhibition of 125I-TGF-beta 1 binding to alpha 2M-methylamine was 50% complete (IC50) with 30 microM ZnCl2. Native alpha 2M, thrombospondin, and alpha 2M-methylamine (in solution) decreased binding of 125I-TGF-beta 1 to immobilized alpha 2M-methylamine. The IC50 values for these three proteins were 520, 160, and 79 nM, respectively. The TGF-beta 1-binding activity of native alpha 2M may have reflected, at least in part, trace-contamination with alpha 2M-proteinase complex.

The influence of site-specificity of single amino acid substitutions on electrophoretic separation of yeast iso-1-cytochrome c

This study dealt with the ability of non-denaturing gel electrophoresis to separate iso-1-cytochrome c with single amino acid replacements isolated from revertants of various cyc1 nonsense mutants of the yeast Saccharomyces cerevisiae. A total of 28 different iso-1-cytochromes c with single amino acid substitutions of one of seven amino acids at six positions were examined on nondenaturing polyacrylamide gels at pH 4.8. Each of these iso-1-cytochromes c exhibited 1 of 16 distinct electrophoretic mobilities. We could distinguish the majority of iso-1-cytochromes c, even those having the same replacement at different sites and those having different replacements that resulted in the same net charge. These results provide confirmation of the importance of site-specific effects on the electrophoretic mobility, and presumably other properties, of proteins differing in sequence by as little as one amino acid. They demonstrate that nondenaturing electrophoresis is able to separate the majority of, but not all, proteins differing by single amino acids.

The presence of two forms of the phosphocarrier protein HPr of the phosphoenolpyruvate:sugar phosphotransferase system in streptococci

The protein, HPr, a necessary component of the phosphoenolpyruvate phosphotransferase system (PTS) in bacteria, was purified from Streptococcus salivarius by column chromatography. The purified preparation gave only one band when analyzed by sodium dodecylsulfate gel electrophoresis or by isoelectric focusing in polyacrylamide gel (pI = 4.85). However, electrophoresis in Tris-containing buffers under non-denaturing conditions revealed 2 bands that could be phosphorylated by PEP in the presence of enzyme I of the PTS or by ATP with the HPr kinase. Homogeneous preparations of these 2 forms could be obtained by preparative electrophoresis. Each preparation exhibited only 1 band when analyzed by electrophoresis under non-denaturing conditions, indicating that the doublet observed before preparative electrophoresis was not an electrophoretic artefact. The electrophoretic mobility of each protein was not modified following heat-treatment at 100 degrees C for 20 min or storage at -40 degrees C for several months. Both HPr proteins catalyzed in vitro the PEP-dependent phosphorylation of glucose, but at a rate slightly lower than that observed with a preparation of HPr containing both forms of the protein. Both forms were also able to transfer the phosphate group from PEP to the other specific PTS proteins known in S salivarius. Rabbit polyclonal antibodies directed against each form reacted with both proteins. The presence of the 2 forms of HPr was detected in fresh cellular extracts of S salivarius; however, their intracellular ratio varied according to growth conditions. A doublet was also found in many other streptococcal species tested (S mutans, S sobrinus, S sanguis, S thermophilus, S bovis, S rattus) and also in L lactis.(ABSTRACT TRUNCATED AT 250 WORDS)

Soluble fibrin preparations inhibit the reaction of plasmin with alpha 2-macroglobulin. Comparison with alpha 2-antiplasmin and leupeptin

The kinetics of plasmin inhibition by alpha 2-antiplasmin (alpha 2AP), alpha 2-macroglobulin (alpha 2M) and leupeptin were studied in the presence of fibrin monomer (Fn) and CNBr fragments of fibrinogen (Fg-CNBr). Active plasmin was detected in continuous and discontinuous assays using the chromogenic substrate D-Val-L-Leu-L-Lys p-nitroanilide hydrochloride (S-2251). The two 'fibrin-like' preparations functioned as hyperbolic mixed-type inhibitors of S-2251 hydrolysis. The dissociation constants (KF) for the binding of plasmin to Fn and Fg-CNBr were 22 nM and 17 nM respectively. Fn and Fg-CNBr inhibited the reaction of plasmin with alpha 2AP: the extent of inhibition depended on the fibrin concentration. In the presence of 800 nM-Fn or 800 nM-Fg-CNBr, the experimental second-order rate constant (K"app.) was decreased from 2.4 x 10(7) M-1.s-1 to 1.2 x 10(6) and 5.3 x 10(5) M-1.s-1 respectively. The effect of Fn and Fg-CNBr on the rate of plasmin inhibition by alpha 2M was even greater. The k"app. value was decreased from 4.0 x 10(5) M-1.s-1 to 8.0 x 10(2) and 1.3 x 10(3) M-1.s-1 in the presence of 800 nM-Fn and -Fg-CNBr respectively. By contrast, the fibrin preparations caused only a small change in the rate of plasmin inhibition by leupeptin. The maximum change in k"app. was 3-fold. All plasmin inhibition curves were linear, suggesting that free and fibrin-bound forms of plasmin remained in equilibrium during the course of reaction with proteinase inhibitors. Fn and Fg-CNBr had no effect on the reaction of miniplasmin with S-2251, alpha 2AP or alpha 2M. When 125I-plasmin was incubated with Fg-CNBr and then allowed to react with a premixed solution of alpha 2AP and alpha 2M, the Fg-CNBr did not significantly change the percentage of plasmin bound to alpha 2AP. These experiments demonstrate that the reaction of plasmin with alpha 2M is inhibited by the non-covalent binding of plasmin to fibrin. We propose that plasmin bound to the surface of a clot is protected from inhibition by alpha 2M as well as by alpha 2AP.

(Mg-ATP)-dependent self-assembly of molecular chaperone GroEL

The important Escherichia coli heat-shock protein GroEL of relative molecular mass 57,259 is a typical molecular chaperone. It possesses ATPase activity and interacts in ATP-driven reactions with non-folded proteins to stimulate their correct folding and/or assembly by preventing the formation of improper protein structures or aggregates. As GroEL is isolated and functions as a 20-25S tetradecameric particle (GroELp), the question arises--what is the mechanism of its own assembly? Here we show the (Mg-ATP)-dependent self-stimulation ('self-chaperoning') in vitro of GroELp reassembly from its monomeric state.

The structure of alpha 2-macroglobulin-methylamine after papain digestion as determined by electron microscopy

alpha 2-Macroglobulin-methylamine (alpha 2M-CH3NH2) was digested with papain at pH 5.0. The major 600 kDa fragment was purified by molecular-exclusion chromatography. In a non-denaturing gel-electrophoresis system, the 600 kDa fragment migrated in a single band at a rate that was comparable with that for the untreated alpha 2M-CH3NH2. The elution volume of the 600 kDa fragment on Superose-6 was slightly increased. In primary cultures of rat hepatocytes, cellular uptake of 125I-alpha 2M-CH3NH2 was not affected by the 600 kDa fragment, confirming the results of other investigators. The 600 kDa fragment was negatively stained with uranyl formate and analysed by transmission electron microscopy. The major structural characteristics of the parent protein (alpha 2M-CH3NH2) remained intact. The most common image included prominent lateral walls and two centrally located regions of stain exclusion termed 'paddle structures'. The distance between the paddle structures was equivalent in alpha 2M-CH3NH2 and the 600 kDa fragment [approximately 13.5 nm (135 A)]. By contrast, the lateral walls in the 600 kDa fragment were decreased in length by approximately 0.37 nm (37 A) (19%). It is proposed that the 600 kDa structure retains the 'hollow cylinder' shape of alpha 2M-CH3NH2. The structure of the cylinder is formed by the lateral walls and four paddle structures (only two are imaged, owing to overlapping). The paddle structures in the 600 kDa fragment are intact and relatively closer to the apices of the molecule, owing to the decrease in lateral wall length. Since the alpha 2M receptor-binding sites are removed by papain digestion, the studies presented here support the location of the receptor-binding sites near the apices of the lateral walls.

Secretion of alpha 2-macroglobulin, alpha 2-antiplasmin, and plasminogen activator inhibitor-1 by glioblastoma multiforme in primary organ culture

Explants from a glioblastoma multiforme were maintained for 4 weeks in a three-dimensional Gelfoam matrix culture in order to study the synthesis of alpha 2-antiplasmin (alpha 2AP), alpha 2-macroglobulin (alpha 2M), plasminogen activator inhibitor-1 (PAI-1), and tissue plasminogen activator (t-PA). Since the organ culture system promotes cellular differentiation in gliomas with increasing time in vitro, secretion of the proteinase inhibitors and t-PA was examined at weekly intervals. Increased immunohistochemical staining for glial fibrillary acidic protein, a marker of astroglial differentiation, was observed in the explants with advancing time in culture. The proteinase inhibitors alpha 2AP and alpha 2M were secreted into the medium in all 4 weeks, while PAI-1 was detected at significant concentrations by an enzyme-linked immunosorbent assay (ELISA) in Weeks 3 and 4 only. The quantity of each inhibitor secreted into fresh medium during a 24-hour interval increased with the age of the tumor explants in the Gelfoam culture system. At no time was a sensitive ELISA able to detect t-PA in the culture medium. This study demonstrates that glioblastoma multiforme cells in primary organ culture can secrete three major fibrinolysis proteinase inhibitors. The appearance of PAI-1 only after extensive culturing of the explants suggests a possible correlation with neoplastic astroglial maturation.

Plasminogen carbohydrate side chains in receptor binding and enzyme activation: a study of C6 glioma cells and primary cultures of rat hepatocytes

The human [Glu1]-plasminogen carbohydrate isozymes, plasminogen type I (Pg 1) and plasminogen type II (Pg 2), were separated by chromatography and studied in cell binding experiments at 4 degrees C with primary cultures of rat hepatocytes and rat C6 glioma cells. In both cell systems, Pg 1 and Pg 2 bound to an equivalent number of receptors, apparently representing the same population of surface molecules. The affinity for Pg 2 was slightly higher. With hepatocytes, the KD for Pg 1 was 3.2 +/- 0.2 microM, and the KD for Pg 2 was 1.9 +/- 0.1 microM, as determined from Scatchard transformations of the binding isotherms. The Bmax was approximately the same for both isozymes. With C6 cells, the KD for Pg 1 was 2.2 +/- 0.1 microM vs. 1.5 +/- 0.2 microM for Pg 2. Again, the Bmax was similar with both isozymes. 125I-Pg 1 and 125I-Pg 2 were displaced from specific binding sites by either nonradiolabeled isozyme. The KI for Pg 2 was slightly lower than the KI for Pg 1 with hepatocytes (0.9 vs. 1.3 microM) and with C6 cells (0.6 vs. 1.1 microM). No displacement was detected with miniplasminogen at concentrations up to 5.0 microM. Activation of Pg 1 and Pg 2 by recombinant two-chain tissue-plasminogen activator (rt-PA) was enhanced by hepatocyte cultures. The enhancing effect was greater with Pg 2. Hepatocyte cultures did not affect the activation of miniplasminogen by rt-PA or the activation of plasminogen by streptokinase. Unlike the hepatocytes, C6 cells did not enhance the activation of plasminogen by rt-PA or streptokinase; however, plasmin generated in the presence of C6 cells reacted less readily with alpha 2-antiplasmin.

Kinetics of the reaction of streptokinase-plasmin complex with purified human and mouse alpha 2-macroglobulin. Implications for mechanism

Streptokinase-human plasmin complex (Sk-hPm) reacted rapidly with purified mouse alpha 2-macroglobulin (m alpha 2M) in vitro at 37 degrees C. Approx. 98% of the plasmin in Sk-hPm bound covalently to at least one m alpha 2M subunit. Most of the streptokinase dissociated (95%). The rate of Sk-hPm inactivation clearly depended on the m alpha 2M concentration. With 1.2 microM-m alpha 2M, 50% of the Sk-hPm (0.02 microM) reacted in less than 50 s. A double-reciprocal plot comparing pseudo-first-order rate constants (kapp.) and m alpha 2M concentration yielded a second-order rate constant of 2.3 x 10(4) M-1.s-1 (r = 0.97). This value is an approximation, since Sk-hPm preparations are heterogeneous. Sk-hPm reacted with human alpha 2M (h alpha 2M), forming alpha 2M-plasmin complex (98% covalent). More than 99% of the streptokinase dissociated. The rate of reaction of Sk-hPm with h alpha 2M did not clearly depend on inhibitor concentration. The kapp. values determined with 0.6-1.2 microM-h alpha 2M were decreased 10-20-fold compared with m alpha 2M. In order to study the effect of Sk-hPm heterogeneity on the reaction with alpha 2M, the proteinase was incubated for various amounts of time at 37 degrees C before addition of inhibitor. The enzyme amidase activity was maximal within 5 min; however, reaction of Sk-hPm with m alpha 2M or h alpha 2M was most extensive after 20 min and 2 h respectively. After incubation for more than 1 h, Sk-hPm acquired fibrinogenolytic activity, suggesting plasmin dissociation. Therefore the enhanced reaction of h alpha 2M with 'older' Sk-hPm preparations may have resulted in part from dissociated plasmin or 'plasmin-like' species. By contrast, the reaction of Sk-hPm with m alpha 2M was most rapid when the proteinase preparation was free of plasmin, indicating direct reaction of Sk-hPm with m alpha 2M as the only major mechanism. Finally, streptokinase-cat plasminogen complex reacted more extensively with m alpha 2M than with h alpha 2M, suggesting that m alpha 2M may be a superior inhibitor with this class of plasminogen activators in general.

Binding of bovine, ovine, porcine, canine, and rat plasminogen to rat hepatocytes and rat C6 glioma cells in vitro

Plasminogens were purified by affinity chromatography from bovine, ovine, porcine, canine, and rat plasma. The binding of each plasminogen to rat hepatocytes in primary culture and to rat C6 glioma cells was studied by radiodisplacement experiments. All of the plasminogens inhibited human 125I-[Glu1]plasminogen type 2 binding to specific cell surface receptors. The IC50 values were similar. These studies suggest conservation of the receptor recognition site in plasminogens across species lines.

Cleavage of recombinant murine interferon-gamma by plasmin and miniplasmin

Plasmin reacted readily with recombinant murine interferon-gamma (rIFN-gamma) in vitro, reducing the relative molecular mass of each monomer by approximately 1,000. The amino terminus of the rIFN-gamma remained intact and no sites of internal peptide bond hydrolysis were detected, indicating that the plasmin target region is most likely near the carboxyl terminus. Cleavage of rIFN-gamma was observed with similar concentrations of trypsin or min-plasmin. By contrast, human neutrophil elastase failed to alter the structure of rIFN-gamma. The plasma proteinase inhibitor, alpha 2-antiplasmin, protected rIFN-gamma from plasmin digestion. Purified alpha 2-macroglobulin-plasmin complex cleaved rIFN-gamma; however, the activity was greatly reduced compared with the free proteinase. The antiviral activity of the rIFN-gamma was enhanced four- to fivefold by treatment with plasmin or trypsin. By contrast, naturally occurring murine IFN-gamma was inactivated by plasmin (80%), suggesting that the effect of plasmin on IFN activity can vary depending on the preparation studied. The importance of plasmin at the site of an immune reaction is well established. This investigation identifies plasmin and miniplasmin as physiologic proteinases capable of reacting with IFN-gamma in vivo.

Independent analysis of bait region cleavage dependent and thiolester bond cleavage dependent conformational changes by cross-linking of alpha 2-macroglobulin with cis-dichlorodiammineplatinum(II) and dithiobis(succinimidyl propionate)

Treatment of the human plasma proteinase inhibitor alpha 2-macroglobulin (alpha 2M) with proteinase results in conformational changes in the inhibitor and subsequent activation and cleavage of the internal thiolester bonds of alpha 2M. Previous studies from this laboratory have shown that cross-linking the alpha 2M subunits with cis-dichlorodiammineplatinum(II) (cis-DDP) prevents the proteinase-induced conformational changes which lead to the activation and cleavage of the internal thiolester bonds of alpha 2M. In addition, cis-DDP treatment prevents the proteinase- or CH3NH2-induced conformational changes in alpha 2M which lead to a "slow" to "fast" change in nondenaturing polyacrylamide gel electrophoresis. In this paper, we demonstrate that treatment of alpha 2M with dithiobis(succinimidyl propionate) (DSP) also results in cross-linking of the subunits of alpha 2M with concomitant loss of proteinase inhibitory activity. Although proteinase is not inhibited by DSP-treated alpha 2M, bait region specific proteolysis of the alpha 2M subunits still occurs. Unlike cis-DDP-treated alpha 2M, however, incubation of DSP-treated alpha 2M with proteinase does not prevent the bait region cleavage dependent conformational changes which lead to activation and cleavage of the internal thiolester bonds in alpha 2M. On the other hand, cross-linking of alpha 2M with DSP does prevent the conformational changes which trigger receptor recognition site exposure following cleavage of the alpha 2M thiolester bonds by CH3NH2. These conformational changes, however, occur following incubation of the CH3NH2-treated protein with proteinase.(ABSTRACT TRUNCATED AT 250 WORDS)

Inactivation of alpha 2-antiplasmin by limited reaction with cis-dichlorodiammineplatinum (II)

alpha 2-Antiplasmin (alpha 2AP), a serpin proteinase inhibitor with two methionine residues in its reactive center, was treated with cis-dichlorodiammineplatinum (II) (cis-DDP). This compound has been utilized previously to specifically modify methionine residues. After reaction, the alpha 2AP demonstrated decreased inhibitory activity against plasmin, miniplasmin, trypsin and chymotrypsin. The reduction in activity depended on the concentration of cis-DDP; however, the amount of activity retained by the treated alpha 2AP was equivalent with each of the four proteinases. alpha 2AP that was incubated with 1.0 mM cis-DDP for 3 h at 37 degrees C was 90% inactivated. These same conditions resulted in the binding of only 1.0-1.5 mol of platinum per mol of inhibitor. In experiments with lower concentrations of cis-DDP, the amount of incorporated platinum directly correlated with the amount of inactivated alpha 2AP (1:1 stoichiometry). Reactions and functions of alpha 2AP that do not result in proteinase inhibition were not affected by cis-DDP. Cleavage of alpha 2AP by elastase, which occurs near the proteinase inhibition site, was unaffected. In addition, the affinity of alpha 2AP for the K1-3 region of plasminogen remained unchanged after treatment. These data strongly suggest that the reaction of alpha 2AP with cis-DDP involves principally a single site on the inhibitor and that this site is critical for proteinase inhibitory activity. The most likely candidate is the P'1 methionine which is adjacent to the peptide bonds cleaved in the proteinase inhibitory reactions but not in the elastase reaction.

Covalent complexes of albumin with serotonin, ketanserin and lysergic acid antagonize the activity of serotonin in human platelets

Covalent conjugates of bovine serum albumin (BSA) and 5-HT, ketanserin or d-lysergic acid were synthesized and characterized by polyacrylamide gel electrophoresis, whole blood clearance experiments in mice and aggregation studies with human platelets. Using the standard synthesis procedure, each mol of BSA bound 13.4 mol of [3H]5-HT. Derivatization did not cause significant protein aggregation as determined by electrophoresis. All three conjugates antagonized the ability of 5-HT to amplify aggregation caused by low concentrations of ADP. The antagonist activity of each conjugate was concentration dependent; 2.6 microM 5-HT-BSA completely inhibited the aggregation caused by 13 microM 5-HT. None of the BSA drug conjugates, including 5-HT-BSA, amplified platelet aggregation caused by ADP in the absence of 5-HT. Aggregation by ristocetin, collagen, epinephrine or ADP alone was not significantly affected by the conjugates. Whole blood elimination experiments in mice demonstrated that the three conjugates and underivatized BSA are equally stable in the circulation. These prototypic 5-HT drug-protein conjugates may be useful for probing 5-HT2 receptor-ligand interactions in human platelets.

Analysis of thiolester bond cleavage-dependent conformational changes in binary alpha 2-macroglobulin-proteinase complexes

The structures of the two proteinase-binding sites in human alpha 2-macroglobulin (alpha 2M) were probed by treatment of alpha 2M with the serine proteinases thrombin and plasmin. Each proteinase forms an equimolar complex with alpha 2M (a binary alpha 2M-proteinase complex) which results in the activation and cleavage of two internal thiolester bonds in alpha 2M. Binary alpha 2M-proteinase complexes demonstrated an incomplete conformational change as determined by nondenaturing polyacrylamide gel electrophoresis and incomplete receptor recognition site exposure as determined by in vivo plasma elimination studies. Treatment of binary alpha 2M-proteinase complexes with CH3NH2, trypsin, or elastase resulted in cleavage of an additional one or two thiolester bonds in alpha 2M and complete receptor recognition site exposure, demonstrating that a limited conformational change had occurred. Treatment of the alpha 2M-thrombin complex with elastase resulted in the incorporation of approximately 0.5 mol proteinase/mol alpha 2M and completion of the conformational change in the complex. Similar treatment of the alpha 2M-plasmin complex resulted in the incorporation of less than 0.1 mol proteinase/mol alpha 2M. Unlike the alpha 2M-thrombin complex, the alpha 2M-plasmin complex did not undergo a complete conformational change following treatment with CH3NH2 or trypsin. Incubation of this complex with elastase resulted in proteolysis of the kringle 1-4 region of the alpha 2M-bound plasmin heavy chain, and following this treatment the alpha 2M-plasmin complex underwent a complete conformational change. The results of this investigation demonstrate that binary alpha 2M-proteinase complexes retain a relatively intact proteinase-binding site. In the case of the alpha 2M-plasmin complex, however, the heavy chain of alpha 2M-bound plasmin protrudes from the proteinase-binding site and prevents a complete conformational change in the complex despite additional thiolester bond cleavage.

Electrophoresis and electroblotting of native collagens

Electrophoretic and immunoblotting techniques, while now used routinely for the biochemical characterization of many proteins, have not been used for the identification of native collagens. We present here an acidic electrophoresis system using very low percentage acrylamide gels which maintains collagen solubility and allows migration of native dermal collagens. The method gives uniform gels which can be made mechanically stable for subsequent electroblotting. The resulting nitrocellulose transfer allows immunological detection of collagens using either polyclonal or monoclonal antibodies and can be used to screen antibody specificities. The majority of murine monoclonal antibodies directed against collagen bind only to conformational epitopes on the native triple-helical collagen, and thus cannot be screened by Western blotting. This method therefore enables the electrophoretic screening of these monoclonal antibodies and provides an alternative approach for their characterization.

In vivo metabolism of inter-alpha-trypsin inhibitor and its proteinase complexes: evidence for proteinase transfer to alpha 2-macroglobulin and alpha 1-proteinase inhibitor

Inter-alpha-trypsin inhibitor was purified by a modification of published procedures which involved fewer steps and resulted in higher yields. The preparation was used to study the clearance of the inhibitor and its complex with trypsin from the plasma of mice and to examine degradation of the inhibitor in vivo. Unlike other plasma proteinase inhibitor-proteinase complexes, inter-alpha-trypsin inhibitor reacted with trypsin did not clear faster than the unreacted inhibitor. Studies using 125I-trypsin provided evidence for the dissociation of complexes of proteinase and inter-alpha-trypsin inhibitor in vivo, followed by rapid removal of proteinase by other plasma proteinase inhibitors, particularly alpha 2-macroglobulin and alpha 1-proteinase inhibitor. Studies in vitro also demonstrated the transfer of trypsin from inter-alpha-trypsin inhibitor to alpha 2-macroglobulin and alpha 1-proteinase inhibitor but at a much slower rate. The clearance of unreacted 125I-inter-alpha-trypsin inhibitor was characterized by a half-life ranging from 30 min to more than 1 h. Murine and human inhibitors exhibited identical behavior. Multiphasic clearance of the inhibitor was not due to degradation, aggregation, or carbohydrate heterogeneity, as shown by competition studies with asialoorosomucoid and macroalbumin, but was probably a result of extravascular distribution or endothelial binding. 125I-inter-alpha-trypsin inhibitor cleared primarily in the liver. Analysis of liver and kidney tissue by gel filtration chromatography and sodium dodecyl sulfate gel electrophoresis showed internalization and limited degradation of 125I-inter-alpha-trypsin inhibitor in these tissues. No evidence for the production of smaller proteinase inhibitors from 125I-inter-alpha-trypsin inhibitor injected intravenously or intraperitoneally was detected, even in casein-induced peritoneal inflammation. No species of molecular weight similar to that of urinary proteinase inhibitors, 19,000-70,000, appeared in plasma, liver, kidney, or urine following injection of inter-alpha-trypsin inhibitor.

The sensitivity of isoelectric focusing and electrophoresis in the detection of sequence differences in proteins

Fourteen myoglobins of known sequence were examined by isoelectric focusing with and without urea. The 14 sequences formed six distinct mobility classes on gels without urea and three classes on those with urea. For these proteins, isoelectric focusing provides no advantage over single, nonequilibrium, nondenaturing gels in the total number of distinguishable mobility classes. Only major charge differences, resulting from the changes in the total numbers of acidic and basic amino acids, can be detected on gels with urea, indicating that denaturation by urea alters proteins so that small differences in ionization are eliminated.

Purification and characterization of human alpha 2-macroglobulin conformational variants by non-ideal high performance size-exclusion chromatography

Human alpha 2-macroglobulin (alpha 2M) was eluted as a single nondispersed peak from a TSK-G4000SW size exclusion chromatography column equilibrated in 20 mM-sodium phosphate/100 mM-NaCl, pH 7.2 (PBS). The void volume and total accessible volume of the column were 6.08 ml and 14.42 ml. The elution volume (Ve) of native alpha 2M was 9.20 +/- 0.04 ml. The Ve was altered minimally by changing the ionic strength or adding ethanol to the equilibration buffer. Ternary alpha 2M-trypsin, containing 2 mol of proteinase/mol of inhibitor, and alpha 2M-methylamine failed to be eluted in well-defined peaks when the column was equilibrated in PBS. The majority of either preparation was recovered slowly at Ve values greater than 14.5 ml, reflecting significant nonideal interactions with the support structure. Addition of 10% ethanol or increased ionic strength in the equilibration buffer independently caused either form of reacted alpha 2M to be eluted in a distinct peak at decreased Ve, suggesting that the nonideal interactions included hydrophobic and electrostatic adsorption. When the equilibration buffer was 80 mM-sodium phosphate/320 mM-NaCl, pH 7.2, partial resolution of ternary alpha 2M-trypsin and alpha 2M-methylamine was obtained with a single column run. The Ve values of ternary alpha 2M-trypsin and alpha 2M-methylamine in this buffer were 13.15 +/- 0.08 ml and 11.94 +/- 0.14 ml, respectively. The Ve of native alpha 2M was 8.84 +/- 0.03 ml. The resolving capacity of TSK-G4000SW was exploited to purify native alpha 2M rapidly and efficiently from solutions that contained significant amounts of either ternary alpha 2M-trypsin or binary alpha 2M-trypsin (1 mol of proteinase/mol of inhibitor). This purification was complete within the limits of sensitivity of denaturing and nondenaturing polyacrylamide-gel electrophoresis. alpha 2M-plasmin was well resolved from native alpha 2M. The Ve of alpha 2M-plasmin was 12.88 +/- 0.32 ml in 80 mM-sodium phosphate/320 mM-NaCl, pH 7.2. A number of procedures were used to prepare solutions with up to 90% binary alpha 2M-trypsin. The Ve of binary alpha 2M-trypsin in these various solutions was intermediate between the values of native alpha 2M and ternary alpha 2M-trypsin. The conformations of binary and ternary complex, as reflected by mobility in nondenaturing electrophoresis, were identical, confirming previous results. Finally, in the binary alpha 2M-trypsin complex, the single trypsin cleaved more than two, and as many as all four alpha 2M subunits.

Linkage analysis of Von Recklinghausen neurofibromatosis: chromosomes 4 and 19

This report describes a study that examines the hypotheses of genetic linkage between the autosomal dominant disorder neurofibromatosis (NF) and loci on human chromosomes 4 and 19. Twelve Utah families were evaluated for evidence of possible linkage of NF to six known markers on chromosome 4 and five markers on chromosome 19. Due to previous reports suggesting tight linkage of NF to the GC locus on chromosome 4 and the C3 (linked to myotonic dystrophy) locus on chromosome 19, these two markers were of particular interest. For the Utah families the cumulative LOD score for GC was -4.81 (r = 0.05). Cumulative LOD scores were -0.90 (r = 0.05) and -1.01 (r = 0.05) for C3 serum determinations and a C3 DNA polymorphism respectively. Linkage data is also included on all individual informative families for the GC and C3 loci to specifically address the question of heterogeneity. Linkage data is consistent with, but does not strongly support, the existence of heterogeneity implicating both the GC locus on chromosome 4 and the C3 locus on chromosome 19. A compilation of cumulative LOD scores from this and other current linkage studies produces values that in the absence of heterogeneity refute previous reports for tight linkage of NF to GC and to C3.

Placental alkaline phosphatase types and subtypes determined by agarose gel electrophoresis and separator isoelectric focusing

Two techniques for phenotyping the human placental alkaline phosphatase system were developed: high-voltage agarose-gel electrophoresis and thin-layer separator isoelectric focusing on agarose. These methods enabled a more rapid and sensitive phenotyping of all common phenotypes than the traditionally employed starch-gel electrophoresis. An extended polymorphism of placental alkaline phosphatase was revealed by isoelectric focusing. The existence of two suballeles of Pl1 allele and two suballeles of Pl2 allele was postulated.

Characterization of oligomers of tubulin by two-dimensional native electrophoresis

We and others [Lee et al. (1973) J. Biol. Chem. 248, 7253-7262; Kravit et al. (1982) J. Cell Biol. 95, 344a; Kravit et al. (1984) J. Cell Biol. 99, 188-198] have observed oligomers of tubulin by native polyacrylamide gel electrophoresis (PAGE), even when they were not evident in sedimentation velocity or gel-exclusion chromatography experiments under comparable conditions. Aggregates of tubulin are also seen on native starch gels. Tubulins purified from calf brain, sea urchin egg (Strongylocentrotus purpuratus), and antarctic fish brain (Pagothenia borchgrevinki) give rise to similar distributions of aggregates. Unlike microtubules, these oligomers are relatively insensitive to temperature (5-25 degrees C), pH (6.1-8.8), the absence of excess GTP and/or Mg+2, stoichiometric concentrations of colchicine, and a variety of electrophoresis buffers. These aggregates, once formed during electrophoresis, associate and dissociate slowly. Depending upon the incubation conditions, they give rise to kinetically controlled distributions that appear in two-dimensional native PAGE as a square array of discrete polymeric species. The fastest migrating species (monomers) are often observed to reequilibrate preferentially into the second band. The second band reequilibrates into the fourth, the third band into the sixth, the fourth into the eighth, etc. (The assignment of molecular weights to these species by Ferguson analysis is tentative due to their slow reequilibration.) Thus, a feature of the reequilibration is that association occurs more rapidly than dissociation and each species is occasionally observed to "dimerize." This behavior is suggestive of irreversible aggregation (possibly crosslinking) or of the formation of slowly dissociating aggregates. Although they may be related to the protofilaments of microtubules, these oligomers appear to be another example of nonmicrotubular, polymorphic aggregates of tubulin.

Gel electrophoresis in studies of protein conformation and folding

Electrophoresis through polyacrylamide gels is a useful method for distinguishing conformational states of proteins and analyzing the thermodynamic and kinetic properties of transitions between conformations. Although the relationship between protein conformation and electrophoretic mobility is quite complex, relative mobilities provide qualitative estimates of compactness. Conformational states which interconvert slowly on the time scale of the electrophoretic separation can often be resolved, and the rates of interconversion can be estimated. If the transitions are more rapid, then the electrophoretic mobility represents the equilibrium distribution of conformations. Protein unfolding transitions induced by urea are readily studied using slab gels containing a gradient of urea concentration perpendicular to the direction of electrophoresis. Protein applied across the top of such a gel migrates in the presence of continuously varying urea concentrations, and a profile of the unfolding transition is generated directly. Transitions induced by other agents could be studied using analogous gradient gels. Electrophoretic methods are especially suited for studying small quantities of protein, and complex mixtures, since the different components can be separated during the electrophoresis.

Purification and properties of cinnamoyl-CoA reductase and cinnamyl alcohol dehydrogenase from poplar stems (Populus X euramericana)

Cinnamoyl-CoA reductase and cinnamyl alcohol dehydrogenase were purified to apparent homogeneity from poplar stems (Populus euramericana) and their main properties were studied. Only one form was identified for each enzyme. The reductase corresponded to one polypeptide of molecular weight 36 000 and the cinnamyl alcohol dehydrogenase was constituted of two identical subunits of molecular weight 40 000. These characteristics are in agreement with most of the data obtained for the same enzymes isolated from other plants. The two reductive enzymes are inhibited by thiol reagents and a metal chelator 1,10-phenanthroline. The isoelectric point of the reductase (pH 7.5) and of the dehydrogenase (pH 5.6) were determined by chromatofocusing. The cinnamoyl-CoA reductase exhibit a decreasing affinity towards feruloyl-CoA, sinapoyl-CoA and p-coumaroyl-CoA. The cinnamyl alcohol dehydrogenase, which catalyses the reduction of the three cinnamaldehydes, exhibits its highest efficiency towards coniferaldehyde. In spite of differences in the monomeric composition of lignins from xylem and sclerenchyma the reductive enzymes isolated from these two lignified tissues exhibit the same substrate specificity. Consequently, they do not play an important role in the qualitative control of lignins in poplar tissues.

Molecular charge and electrophoretic mobility in cetacean myoglobins of known sequence

Fourteen myoglobins of known sequence were examined by polyacrylamide gel electrophoresis at five pH values. Gels at each pH divided the sequences into six to eight distinct classes, while the combination of the results of three gels at different pH levels distinguished 13 of 14, or 93%, of the sequences. The relative mobility of the myoglobins in the gels is significantly correlated with the charges of the proteins calculated from the pK values of the ionized groups. Major differences in mobility corresponded to expected differences in charge due to the amino acid substitutions between sequences. In addition to sequences differing in the total number of acidic and basic residues, those differing from each other in the total number of histidines were distinguished on low-pH gels. One pair of sequences differing by the exchange of lysine for arginine was separated on high-pH gels, as predicted from the differences in ionization of these two amino acids. On gels at pH 10.4, there was greater deviation of electrophoretic mobility from charge than on other gels, possibly due to the influence of amino acid substitutions in the neighborhood of lysine residues. Manipulation of the concentration and composition of the gels did not change the separation of the sequences from each other. Examination of myoglobins by gel electrophoresis at a wide range of pH values allows discrimination of nearly all amino acid substitutions and demonstrates the close relationship between titration and relative electrophoretic mobility.

Restricted repair of aflatoxin B1 induced damage in alpha DNA of monkey cells

We have investigated the processing of adducts formed by covalent binding of aflatoxin B1 (AFB1) to DNA in confluent cultures of African green monkey cells. Repair synthesis elicited by AFB1 adducts was deficient in alpha DNA sequences compared to that in bulk DNA, although the initial levels of modification were the same for these DNAs. The removal of the primary initial adduct, AFB1-N7-Guanine, was deficient in alpha DNA and the kinetics of its loss resembled those previously reported for removal from total DNA in xeroderma pigmentosum cells of complementation group A. Spontaneous loss of the AFB1 moiety or the concomitant loss of the guanine to yield an apurinic site account for these results. The formation of the more chemically stable secondary product, AFB1-triamino-Pyrimidine, occurred more rapidly and to a greater extent in alpha DNA than in bulk DNA, probably because of slower removal of the primary product. The excision repair patch size for AFB1 adducts in alpha DNA was only 10 nucleotides compared to 20 nucleotides for repair of AFB1 adducts in bulk DNA. Irradiation of cells with low doses of UV prior to or immediately after treatment with AFB1 increased the rate and extent of removal of AFB1 adducts from alpha DNA to the levels found in the bulk DNA, indicating that the formation of pyrimidine dimers or their repair may alter the chromatin structure of alpha DNA sufficiently to facilitate its repair.