Enhanced responses of the chorda tympani nerve to nonsugar sweeteners in the diabetic db/db mouse

Genetically diabetic db/db mice show greater neural and behavioral responses to sugars than lean control mice. The present study examined chorda tympani responses of db/db mice to nonsugar sweeteners and their inhibition by a sweet response inhibitor, gurmarin. The results showed that responses to sucrose, saccharin, glycine, L-alanine, and D-tryptophan, but not to D-phenylalanine, were approximately 1.5 times greater in db/db mice than in control mice. Treatment of the tongue with gurmarin suppressed responses to these sweeteners in db/db and control mice, but the extent of suppression was considerably smaller in db/db mice. The magnitudes of gurmarin-sensitive components of the response to sweeteners in db/db mice were not significantly different from those in control mice, whereas the magnitudes of gurmarin-insensitive components in db/db mice were about twice as large as those in control mice. These results suggest that the enhancement of chorda tympani responses in db/db mice to sucrose and other nonsugar sweeteners may occur through gurmarin-insensitive membrane components.

Internal motion of lysozyme studied by time-resolved fluorescence depolarization of tryptophan residues

The internal motion of lysozyme was described by the steady-state and time-resolved fluorescence anisotropy of its tryptophan residues. The fluorescence of mutant lysozymes W62Y- and W108Y-lysozyme, in which Trp62 or Trp108 of hen egg white lysozyme was replaced with a tyrosine residue, could be respectively assigned to Trp108 or Trp62 at the longer wavelength region of the total fluorescence spectrum. The segmental motion of Trp62 as shown by its fluorescence anisotropy decay was described with two components originating from the fluctuational rotation of an indole moiety about the Calpha-Cbeta bond and rotational wobble of the peptide segment adjacent to Trp62. Although Trp62 showed a high degree of motional freedom, its motion was significantly suppressed by the interaction of the mutant protein with a trimer of N-acetyl-D-glucosamine. By contrast, the segmental motion of Trp108 is hindered by the local cage structure at temperatures below 30 degreesC, but Relief from restricted motion occurred on the formation of ligand complex or by thermal agitation. Because of overlaps of the fluorescence spectrum, it is difficult to assign the segmental motion of Trp28 or Trp111, the other two tryptophan residues in lysozyme. However, a careful analysis of the fluorescence anisotropy decay of W62Y- and W108Y-lysozyme showed that the fluctuation of the hydrophobic matrix box was greater than that expected from lysozyme's crystal structure, although it was suppressed by the binding of the ligand to the active site of lysozyme.

Alkalinizing water-soluble local anesthetic solutions by addition of cyclodextrin

BACKGROUND AND OBJECTIVES

The use of sodium bicarbonate for alkalinization of local anesthetics to improve their efficacy has some disadvantages including decreased stability of the solutions. The present study was performed to evaluate usefulness of cyclodextrins (CDs) in improving the solubility and stability of local anesthetic solutions at near physiologic pH without precipitation.

METHODS

Solubility of local anesthetics with or without CDs in physiologic saline was investigated by monitoring cloudiness or precipitate formation visually and by recording absorbance at 620 nm. Interaction of anesthetic and CD was also studied spectrophotometrically using spectral change of the drugs associated with the inclusion complex formation.

RESULTS

Cyclodextrins improved the solubility and stability of the four local anesthetics studied (dibucaine, tetracaine, bupivacaine, and lidocaine). In the neutral pH region, the effects of the CDs were more significant with dibucaine and tetracaine, which are more hydrophobic than the other two. A type of effective CD was different for each anesthetic depending partly on the tendency to form inclusion complex with local anesthetic. The local anesthetic solutions solubilized by CDs were found to remain clear for more than 72 hours without any visible precipitation or turbidity at neutral pHs.

CONCLUSIONS

The improved solubility of local anesthetics by adding CD may be caused by inclusion complex formation of CD with local anesthetics. This new preparation for the alkalinized water-soluble anesthetic solutions may be useful for practical application in the clinical setting, although this awaits further study.

Tolerogenic activity of polyethylene glycol-conjugated lysozyme distinct from that of the native counterpart

Conjugation of proteins with polyethylene glycol (PEG) has been reported to make the proteins tolerogenic. Native proteins are also potentially tolerogenic when given without adjuvants. We compared immunotolerogenic activities between PEG-conjugated and native hen egg-white lysozyme (HEL). BALB/c mice were given consecutive weekly intraperitoneal administrations of PEG-conjugated HEL, unmodified HEL or phosphate-buffered saline (PBS), for 3 weeks, then challenged with HEL in Freund's complete adjuvant. The pretreatment with PEG-HEL tolerized both T-cell and humoral responses, while native HEL tolerized only the T-cell response. Immunoglobulin G1 (IgG1) antibody was already elevated in HEL-pretreated mice prior to challenge immunization, followed by suppressed IgG2a and IgG2b, but spared IgG1 production after the antigen challenge, whereas PEG-HEL-pretreated mice produced no antibody in all IgG subclasses prior and subsequent to the antigen-challenge. Production of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) by lymphoid cells in response to HEL in vitro was markedly suppressed in both the antigen-pretreated groups, while suppression of IL-4 production was evident only in PEG-HEL-, not in HEL-pretreated animals. Involvement of suppressor cells in these tolerance states was found to be unlikely, and the immunological property of PEG-HEL differed from deaggregated HEL that was similar to the original HEL. These results suggest a unique immunotolerogenic activity of PEG-conjugated proteins to suppress both T-helper type-1 (Th1)- and Th2-type responses, the result being extensive inhibition of all IgG subclass responses, while tolerance induction by unconjugated soluble proteins tends to be targeted on Th1-, but spares Th2-type responses.

Detection of a local interaction of hen lysozyme under highly denaturing conditions using chemically 13C-enriched methionine resonance

Using hen lysozyme in which the epsilon-carbons of two methionine residues are enriched with 13C nuclei, we found that there is a subtle difference in the chemical shift of the epsilon-carbon resonances between Met 12 and Met 105 in thermally denatured lysozyme without any reduction of disulfide bonds at pD 3.8, and also in reduced S-alkylated lysozyme at pD 3.8 and 35 degrees C. The difference in the chemical shift was abolished on digestion with TPCK-trypsin and the chemical shifts of both resonances converged to that of Met 12, whose chemical shift is identical to that in the randomly coiled state. Therefore, it is suggested that the chemical shift in the epsilon-carbon resonance of Met 105 is different from that in the randomly coiled state due to an interaction involving Met 105. In order to locate the interaction involving Met 105, fragmentation of the reduced S-alkylated lysozyme into the peptides was carried out by means of chemical cleavage or specific endoprotease digestion. As a result, the local interaction of Met 105 or the residues around Met 105 with eleven residues at the C-terminus of lysozyme is suggested to occur.

Construction of a yeast expression system with positive selection for gene insertion in the absence of a specific phenotype

A positive-selection system of cloned inserts in Escherichia coli has been devised using a streptomycin-resistant (Smr) gene and streptomycin-dependent (Smd) E. coli. A vector, pHA394, based on the yeast expression vector pAM82 has the Smr gene, which inactivates streptomycin (Sm) and invalidates the streptomycin dependence, resulting in a very low transformation efficiency. Replacement of the Smr gene by the recombinant vector allows high-frequency transformation. This system was applied to the lysozyme gene. After the yeast secretion signal was fused to the lysozyme gene using an intermediate vector, pHA474, the Smr gene of pHA394 was replaced by the fusion gene, followed by transformation of Smd E. coli. Analysis of the transformants showed that the plasmid gene contained 100% of the lysozyme gene.

Depression of T-cell epitope generation by stabilizing hen lysozyme

Conformational stability of proteins is an important factor that determines their resistance/susceptibility to proteolytic digestion. Intracellular proteolysis is the key step in antigen presentation events for protein antigens; hence, it is likely that increasing protein stability reduces the antigenicity of proteins. We prepared three hen egg white lysozyme derivatives possessing different stabilities by chemical modification to clarify the relationship between conformational stability and the antigenicity of the protein. One of the derivatives was conformationally unstabilized by removing one intramolecular disulfide bond, whereas the two others were stabilized by the addition of an intramolecular cross-link. The antigenicity of these derivatives was evaluated using hen egg white lysozyme-specific T-cell hybridoma cells and a B-lymphoma cell line, A20, as antigen-presenting cells. With an increase in conformational stability, the T-cell response decreased. However, the reduction was not derived from the inefficiency of internalization to A20 cells nor the alteration of antigenicity by chemical modifications. Moreover, from analyses of their susceptibility to proteolysis and the kinetics of presentation of the T-cell epitope, it was confirmed that increasing protein stability led to the depression of T-cell epitope generation by increasing resistance to proteolysis. These results have an important implication in devising a new strategy for manipulating T-cell response by the stability of protein antigen.

Favourable interaction between heavy and light chains arrests the undesirable oligomerization of heavy chains in the refolding of denatured and reduced immunoglobulin G

Recently we developed a slow dialysis method that effectively refolds denatured and reduced immunoglobulin G (IgG) [Maeda, Ueda and Imoto (1996) Prot. Engng 9: 95-100]. This method allows both individual and simultaneous refolding of denatured and reduced H and L chains. Analysis by SDS-polyacrylamide gel electrophoresis revealed that some oligomers were formed through disulfide bonds when H chains were refolded individually. It was also shown that the extent of IgG obtained by rejoining the mixture of refolded H and L chains which had been refolded individually was similar to that obtained by refolding denatured and reduced whole IgG. The results indicated that a favourable interaction between H and L chains prevented formation of H-chain oligomers to yield intact IgG. The present results suggest a mechanism whereby individually folded chains might associate to form IgG molecules in vivo.

An improved method for preparing lysozyme with chemically 13C-enriched methionine residues using 2-aminothiophenol as a reagent of thiolysis

Jones et al. have reported that the epsilon-carbons of methionine residues in myoglobin can be enriched with stable isotope (13C) in two steps, i.e., methylation of methionine residues with 13CH3I in the protein and thiolysis using dithiothreitol [Jones, W.C., Rothgeb, T.M., and Gurd, F.R.N. (1976) J. Biol. Chem. 251,7452-7460]. Using their method, we failed to prepare active lysozyme in which the epsilon-carbons of methionine residues are enriched with 13C, because many side reactions took place under the thiolysis condition (pH 10.5, 37 degrees C). When we employed 2-aminothiophenol as a reagent for thiolysis, the reduction proceeded under a weakly acidic condition to afford fully active lysozyme, in which the epsilon-carbons of two methionine residues were enriched with 13C, in a 30% yield. Analysis of the 13C-edited NOESY spectra of 13C-enriched methionine lysozyme in the absence and presence of a substrate analogue indicated the occurrence of conformational change around Met 105 in lysozyme.

Improvement of the refolding yield and solubility of hen egg-white lysozyme by altering the Met residue attached to its N-terminus to Ser

When hen egg-white lysozyme was produced in Escherichia coli, it possessed an extra methionine residue at the N-terminus (Met(-1)-lysozyme). The Met(-1)-lysozyme showed a decreased refolding yield and solubility compared with the native hen egg-white lysozyme, as the methionine is a hydrophobic amino acid. A Met(-2)Pro(-1) or Met(-2)Ser(-1) sequence was introduced at the N-terminus of hen egg-white lysozyme. The methionine residue in these hen egg-white lysozymes was completely removed by methionine aminopeptidase, as expected, since the penultimate residue was proline or serine. From the analyses of solubility, stability and refolding yield, it was found that an extra Ser residue attached to the N-terminus of hen egg-white lysozyme (Ser(-1)-lysozyme) showed closer characteristics to the native hen egg-white lysozyme than did Met(-1) or an extra Pro residue attached to the N-terminus of hen egg-white lysozyme (Pro(-1)-lysozyme). Moreover, the tertiary conformation of Ser(-1)-lysozyme examined by NMR spectroscopy and its activity were almost identical with those of native hen egg-white lysozyme.

Analysis of the stability of mutant lysozymes at position 15 using X-ray crystallography

His 15 of hen lysozyme is located at the protein surface and is partly buried by the neighboring residues. The side chain of His 15 forms hydrogen bonds with surrounding residues and these hydrogen bonds are somewhat buried. A series of mutant lysozymes at the position 15 (Gly, Ala, Val, and Phe) was prepared, and their stabilities were analyzed by GdnHCl denaturation and X-ray crystallography. The mutants were less stable than the wild type at pH 5.5 and 35 degrees C. In H15G and H15A, X-ray crystallography revealed two fixed water molecules at the mutated region, which formed similar hydrogen bonds to those in the wild type. On the other hand, it was suggested that the hydrogen bonds were disrupted and that several unfavorable van der Waals' contacts occurred in H15V and H15F. Therefore, we concluded that His 15 stabilized the lysozyme structure by forming hydrogen bonds and the best packing with the neighboring residues. Moreover, we found that the method of protein stabilization by increasing the hydrophobicity of an amino acid residue was not always effectively applicable, especially when the residue had formed a hydrogen bond.

A covalent enzyme-substrate adduct in a mutant hen egg white lysozyme (D52E)

A mutant hen egg white lysozyme, D52E, was designed to correspond to the structure of the mutant T4 lysozyme T26E (Kuroki, R., Weaver, L. H., and Matthews B. W. (1993) Science 262, 2030-2033) to investigate the role of the catalytic residue on the alpha-side of the saccharide in these enzymes. The D52E mutant forms a covalent enzyme-substrate adduct, which was detected by electron ion spray mass spectrometry. X-ray crystallographic analysis showed that the covalent adduct was formed between Glu-52 and the C-1 carbon of the N-acetylglucosamine residue in subsite D of the saccharide binding site. It suggests that the catalytic mechanism of D52E mutant lysozyme proceeds through a covalent enzyme-substrate intermediate indicating a different catalytic mechanism from the wild type hen egg white lysozyme. It was confirmed that the substitution of Asp-52 with Glu is structurally and functionally equivalent to the substitution of Thr-26 with Glu in T4 lysozyme. Although the position of the catalytic residue on the beta-side of the saccharide is quite conserved among hen egg white lysozyme, goose egg white lysozyme, and T4 phage lysozyme, the adaptability of the side chain on the alpha-side of the saccharide is considered to be responsible for the functional variation in their glycosidase and transglycosidase activities.

Influence of mutations of the N-cap residue, Gly4, on stability and structure of hen lysozyme

Hen lysozyme, with three alpha-helices (A, B, and C), is a c-type lysozyme. In these lysozymes, Ser24 and Asp88 located at the N-cap position in the B- and C-helix, respectively, are mostly conserved, but residue 4 at the N-cap position in A-helix is variable. To investigate the effect of mutation at position 4 on the stability of hen lysozyme, we prepared five mutant lysozymes and examined their stabilities and structures. Gly4Pro lysozyme (G4P), in which Gly4 was replaced by Pro, was less stable by 8.8 kJ/mol than the wild-type lysozyme, possibly because the side chain at position 7 is shifted away from the A-helix. The other mutant lysozymes were of almost equal stability to the wild-type lysozyme, although the hydrogen bonds of the amide groups at positions N1-N3 in the A-helix were absent or altered. These results indicated that various mutations at the N-cap position in the A-helix would be allowed as long as the negative charge of Glu7 at the N-terminus stabilized the A-helix.

Analysis of the stabilization of hen lysozyme by helix macrodipole and charged side chain interaction

In the N-terminal region of the alpha-helix of the c-type lysozymes, two Asx residues exist at the 18th and 27th positions. Hen lysozyme has Asp18/Asn27 (18D/27N), and we prepared three mutant lysozymes, Asn18/Asn27 (18N/27N), Asn18/Asp27 (18N/27D), and Asp18/Asp27 (18D/27D). The stability of the wild-type (18D/27N) lysozyme supported the existence of a hydrogen bond between the side chain of Asp18 and the amide group at the N1 position in the alpha-helix, while the stability of the 18N/27D lysozyme supported the presence of the capping box between the Ser24 (N-cap) and Asp27 residues. Although electrostatic repulsion was observed between Asp18 and Asp27 residues in 18D/27D lysozyme, the dissociation of each residue contributed to stabilizing the B-helix in 18D/27D lysozyme through hydrogen bonding and charge-helix macrodipole interaction. This is the first evidence that two neighboring negative charges at the N-terminus of the helix both increased the stability of the protein.

Prevention of collagen-induced arthritis (CIA) by treatment with polyethylene glycol-conjugated type II collagen; distinct tolerogenic property of the conjugated collagen from the native one

Administration of a soluble protein into animals prior to challenge immunization induces immunological tolerance which is specific for the protein. In addition, chemical modification of proteins with polyethylene glycol (PEG) has been reported to convert the immunogenic proteins to become tolerogenic. However, differences in tolerogenic properties between PEG-modified proteins and the native counterparts have never been analysed. The ability of PEG-conjugated type II collagen (PEG-CII) to attenuate CIA, an animal model for rheumatoid arthritis, was compared with the native unconjugated CII. Groups of DBA/1 J mice were treated weekly with i.p. injections with PEG-CII, native CII, or vehicle alone for 3 weeks, before they were challenged with CII in adjuvants. The induction of tolerance was confirmed in both PEG-CII- and CII-pretreated mice when suppression of lymph node T cell proliferation in response to CII was noted. The degrees of suppression of T cell proliferation were comparable between the two pretreated groups. However, induction of arthritis and production of IgG anti-CII antibody were more markedly suppressed in PEG-CII-pretreated mice than in native CII-pretreated mice, although the severity of arthritis and antibody levels in the latter group were also lower than in control mice. IgG2a and IgG2b antibody levels were equally suppressed in the two pretreated groups, whereas the IgG1 level was significantly lower in the PEG-CII-pretreated group than in the native CII-pretreated group. The results provide the first evidence that attachment of PEG to CII renders the protein more tolerogenic.

Stabilization of protein

The stabilization of proteins is discussed from the theoretical and practical points of view. Methods are described for kinetic stabilization and protection from deterioration, as well as the thermodynamic stabilization of proteins.

Lack of gurmarin sensitivity of sweet taste receptors innervated by the glossopharyngeal nerve in C57BL mice

Effects of a sweet response inhibitor, gurmarin, on responses of the chorda tympani and glossopharyngeal nerves were studied in the C57BL/KsJ strain of mice. The lingual application of gurmarin at 3.0 microg/ml (approxiamtely 0.7 microM) or more significantly suppressed chorda tympani responses to 0.5 M sucrose, as previously reported. The magnitude of gurmarin inhibition of the chorda tympani responses reached a plateau (approximately 45% of control) at 50 microg/ml (approximately 11.9 microM). In contrast, no such gurmarin inhibition of sucrose responses was observed in the glossopharyngeal nerve even at 100 microg/ml (approximately 23.8 microM). The lingual application of a proteolytic enzyme, pronase, suppressed sucrose responses to <20% of control in both chorda tympani and glossopharyngeal nerves. These results suggest differential sensitivity to gurmarin by sweet taste receptors innervated by the chorda tympani and the glossopharyngeal nerves. The former apparently possess gurmarin sensitivity, whereas most of the latter may be lacking sensitivity.

Quaternary structure-dependent idiotope and antigen binding of a monoclonal antibody specific for conformational epitope on type II collagen

We previously generated a monoclonal antibody (mAb) against a putative pathogenic epitope on native type II collagen (CII) for the induction of collagen-induced arthritis in mice (mAb1), and an anti-idiotypic mAb which appears to possess the internal image of the CII epitope (mAb2). In the present study, the structural basis of the antigen/mAb1 and mAb1/mAb2 interactions was examined. When partially SH-reduced mAb1 was analysed on Western blots, only fragments containing both heavy (H) and light (L) chains were recognized by mAb2. When mAb2 was partially SH-reduced, only fragments containing both H and L chains were recognized by mAb1. H and L chains were separated from mAb1 in a reduced, denatured condition, and each chain and a mixture of the two were refolded. mAb2 reacted specifically to the renatured whole IgG molecule of mAb1, but not to the refolded L or to H chains. Recombinant single chain Fv (scFv) generated from mAb1 and mAb2 had properties of the original mAbs, whereas genetically constructed chimeric scFvs, consisting of VH from mAb1 and an irrelevant VL. or VL of mAb1 and an irrelevant VH. did not react either to CII or to mAb2. Thus, interactions among CII, mAb1 and mAb2 appear to depend on quaternary structures containing different protein subunits. These observations support the internal image property of the mAb2. In addition, this dependency on quaternary structure for recognition of proteins may also be relevant to other protein-protein interactions.

Identification of the peptide region that folds native conformation in the early stage of the renaturation of reduced lysozyme

We prepared three peptide fragments (fg.59-105, fg.63-105 and fg.64-105) by the BrCN cleavage of mutant lysozymes where Ile58, Trp62 and Trp63 were mutated to Met, respectively. From the analysis of formation of the disulfide bonds among Cys64, Cys76, Cys80 and Cys94 in the renaturation of each peptide fragment from the reduced form, Trp62 and Trp63 were required for the effective formation of two disulfide bonds. Especially, Trp62 was found to be involved in the correct formation of the disulfide bonds.

Analysis of the transition state in the unfolding of hen lysozyme by introduction of Gly-Pro and Pro-Gly sequences at the same site

We developed a sensitive method for analyzing the conformation of the transition state in the unfolding of hen lysozyme. The activation free energy changes of mutant lysozymes with Gly-Pro and Pro-Gly sequences at the same sites (Gly47Pro47', Pro47Gly47', Gly101Pro102, Pro101Gly102, Gly117Pro118, Pro117Gly118, Gly121Pro122, and Pro121Gly122 lysozymes) were obtained for the unfolding in aqueous solution at pH 5.5 and 35 degrees C. Since we had shown that the difference of energies of the unfolded state in lysozymes having an introduced Gly-Pro or Pro-Gly sequence at the same site was much smaller than the difference of energies of the folded states [Motoshima, H., Ueda, T., Hashimoto, Y., Tsutsumi, M., and Imoto, T. (1995) J. Biochem. 118, 1138-1144], we could estimate the difference of energies of the folded and the transition states unequivocally. We defined the phi-value as the ratio of the difference in the free energy change in the transition state to that in the free energy change in the folded state between lysozymes with Gly-Pro and Pro-Gly sequences at the same site. The phi-values gave information on how much the mutated sites retained the folded structure in the transition state. These values were 0.45 around position 47, which is located in the beta-sheet structure, 0.12 at position 101-102, which is located in the loop at the upper part of the active site, 0.17 at position 117-118, which is located in the beta-turn and 0.64 at position 121-122, which is located in the 3(10)-helix. Therefore, in the transition state in the unfolding of lysozyme, it was found that the 3(10)-helical region had a similar structure to the intact region, while both the beta-turn and the loop at the upper part of the active site were considerably unfolded. The beta-sheet structure was also moderately disrupted in the transition state.

Situation of monomethoxypolyethylene glycol covalently attached to lysozyme

We selectively introduced monomethoxypolyethylene glycol (mPEG) 5000, 2000, and 550 into Asp119 in lysozyme. To examine how the mPEGs were present on the surface of the modified lysozyme, the activities, binding abilities to the Fab fragment of anti-lysozyme monoclonal antibody, net charges and nuclear magnetic resonance (NMR) spectra of mPEG lysozymes were examined. With the increase in molecular weight of mPEG, the activities and binding abilities to the Fab of mPEG lysozyme decreased. However, introduced mPEG5000 did not cause complete inhibition of the activities and binding abilities to the Fab, while the maximum length of mPEG5000 was so great that it largely covered the surface of the lysozyme molecule. Analyses of the net charges and NMR suggested that the introduced mPEG preferentially assumed a folded conformation on the surface rather than spread all over the surface. Based on the structure of mPEG lysozyme, the mechanism of the reduced immunogenicity of mPEG lysozyme was discussed.

Effect of additives on the renaturation of reduced lysozyme in the presence of 4 M urea

Reduced lysozyme was renatured by sulfhydryl-disulfide interchange reactions at pH 8.0 in the presence of 4 M urea, with or without additives at 40 degrees C. In the absence of additives, the final folding yield of reduced lysozyme was approximately 40%. In the presence of sarcosine, glycerol, ammonium sulfate, N-acetyl glucosamine and glucose, its folding yields increased in all cases. In particular, yields increased up to 90% in the presence of 4 M sarcosine. On the other hand, the melting temperatures of lysozyme with or without additives in 0.02 M citrate buffer (pH 6.0) were evaluated using differential scanning calorimetry. In the absence of additive, the melting temperature of lysozyme was 73.8 degrees C. In the presence of additives, all melting temperatures were higher than that of lysozyme in the absence of additives. Moreover, there was a good correlation on addition of additives between an increase in the folding yield of reduced lysozyme with 4 M urea and an increase in the melting temperature without 4 M urea. Therefore, we conclude that additives, which stabilize native lysozyme, are effective at increasing the folding yield of reduced lysozyme in 4 M urea.

Severe endurance training fails to change myosin heavy-chain distribution of diaphragm

Histochemical analysis by Green et al. (1989) revealed that severe endurance training caused a transformation from type IIA to type IIB fibres in the costal diaphragm region of the rat. With the use of the electrophoretic method, in the current study, it was re-examined whether such a change was brought about in this respiration muscle. The animals were capable of running for 240 min/day at 40 m/min during the final phase of a 16-week training program. Four heavy-chain (HC) isoforms were separated by a single percentage polyacrylamide gel electrophoresis of extracts from muscles. Densitometric analysis of these HC isoforms revealed that exercise training failed to change the relative distribution of any HC isoforms in the diaphragm.

[Establishment of fundamentals for protein research. Stabilization of protein]

Proteins are usually in an equilibrium between the folded and the unfolded state. Therefore, for the stabilization of proteins against reversible denaturation, the free energy change for the unfolding should be increased by stabilizing the folded state by lowering the energy level of the folded state or by destabilizing the unfolded state by raising the energy level of the unfolded state. On the other hand, various processes can be coupled with the unfolded state of proteins. For example, protease digestion of proteins at physiological temperature may be one of such processes. The process would lead to an irreversible denaturation. For the stabilization of proteins against the irreversible denaturation coupled with the unfolded state, a kinetic stabilization is important, that is, the activation free energy for the unfolding should be increased. Methods for the kinetic stabilization were discussed. Finally, the irreversible chemical deterioration of proteins was considered.