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Biomedical subjects

S Sugai

Publications and source records attributed to S Sugai.

At least 235 records · Page 13Linked to original sources
PubMed1980

Intramolecular perturbation of tryptophans induced by the protonation of ionizable groups in goat alpha-lactalbumin.

Goat alpha-lactalbumin shows two septral changes at acid pH. One of these corresponds to the acid denaturation, while the other has been regarded as a result of the intramolecular perturbation of tryptophans induced by the protonation of ionizable groups in the native molecule. In order to distinguish between these spectral changes and to investigate the perturbation caused by the ionizable groups, the absorption changes with a change in pH have been followed by the stopped-flow pH-jump method. Only the acid denaturation can be observed kinetically while the perturbation is too rapid to follow by the kinetic method. Extrapolations of the time-dependent absorption changes to zero time in the unfolding and refolding pH jumps give the apparent titration curves of the ionizable groups that participate in the perturbations in the native and in the acid-denatured molecule. The perturbation of the native protein is induced by the protonation of at least two ionizable groups, while the acid-denatured molecule does not show the perturbation because of the loss of the unique spatial arrangement of the ionizable groups around tryptophans. The results of circular dichroism measurements and the comparison with known results of the charge perturbation of lysozyme are also discussed.

Animals↗
PubMed1980

Non-IgM monoclonal gammopathy in patients with Sjögren's syndrome.

Two Japanese patients with Sjögren's syndrome with non-immunoglobulin M(IgM) class monoclonal gammopathy are described. The monoclonal IgA lambda detected in the serum and saliva was confirmed to possess rheumatoid factor activity in the first patient with a hypergammaglobulinemic purpura and hyperviscosity syndrome. Idiotype specificity was present on the surface membrane of peripheral blood lymphocytes as well as in the cytoplasm of infiltrating cells in the salivary glands. Common idiotypic specificity was found in four of 60 other patients who had rheumatoid factors. In the serum and saliva of the other patient, a monoclonal immunoglobulin G, kappa type (IgG kappa), was detected. Kappa type IgG was found in most of the infiltrating cells in the salivary glands and also in the saline extract from a resected submandibular gland. Our findings indicate that non-IgM class monoclonal gammopathy is also one of the complications of Sjögren's syndrome.

Female↗
PubMed1980

Conformational transitions of the hydrophobic polyacids.

The conformational transitions of the alternating maleic acid copolymers with styrene (MA-St)n, and alpha-methyl styrene (MA-MSt)(n) in aqueous solutions were studied by means of various methods. The following results were obtained: 1) The conformational transitions of (MA-St)n from the compact to extended coil form are observed in various salt solutions, as in aqueous NaCl, and the compact form is stabilized by Rb+ and Cs+, but destabilized by Li+. The coions, Br-, I-, ClO4- and SCN- affect scarcely the stability of the compact form. 2) The temperature coefficient of viscosity d In [eta]/dT of (MA-St)n in 0.09 M NaCl was positive for the compact form, but negative for the coil form, and it reflects the transition. 3) The difference between specific heats for the compact and coil forms of (MA-St)n in 0.03 M NaCl is determined to be about 15% of the corresponding heat of transfer of benzene to aqueous medium. 4) A remarkable dilution of the bound monomeric acridine orange to the compact form (MA-St)n is observed and the dimerization free energy of the dye in the compact form is about -2.1 kcal mole at 25 degrees C. 5) Potentiometric, dilatometric and viscometric titrations of (MA-MSt)n in aqueous NaCl at 25 degrees C show a similar conformational transition to that of (MA-St)n. Also, the difference in the molar extinction coefficient at 261 nm indicates the transition. The compact form of (MA-MSt)n is more unstable than that of (MA-St)n. From the results, the compact conformations and the transition mechanism of both the polyacids were discussed in comparison with the results for the maleic acid copolymers with n-alkyl vinyl ethers.

Journal Article↗
PubMed1980

Folding of yeast 5S ribosomal RNA induced by magnesium binding.

The magnesium-induced conformational changes of yeast 5S ribosomal RNA have been studied by means of difference absorption spectroscopy and circular dichroism. A hypochromic difference absorption spectrum with a trough at approximately 260 nm was observed together with a slight increase and blue shift of the peak at 265 nm and a significant increase of the absolute magnitude of the trough at 208 nm in the circular dichroism spectrum. The magnesium concentration dependence of the difference absorption gave a Hill coefficient of 2.0 +/- 0.2. All of the equilibrium data indicate that magnesium ions produce a more ordered form of the molecule. Transient kinetic studies using a magnesium concentration-jump were carried out. The kinetic curves were biphasic, each phase being associated with a relatively slow unimolecular conformational change induced by magnesium binding. A simple scheme was able to accommodate all of the equilibrium and kinetic data, and the kinetic parameters were calculated. Activation parameters for the unimolecular steps suggest that the conformational changes of the 5S RNA involved the breaking of several base pairs and tertiary folding.

Circular Dichroism↗
PubMed1979

Application of the pH-jump method to the titration of tyrosine residues in bovine alpha-lactalbumin.

A stopped-flow technique has been developed for the zero-time spectrophotometric titration of tyrosine residues in the purely native or in the purely alkaline denatured state of alpha-lactalbumin that undergoes an alkaline conformational transition in the pH region of tyrosine ionization. The progressive absorption change at 298 nm caused by a pH jump from neutral pH is shown to result from the change in ionization of the tyrosine residues brought about by a first-order process of the conformational transition. Extrapolation to zero time gives the titration curve for purely native alpha-lactalbumin. Similarly, the pH jump from highly alkaline pH gives the titration curve for the purely alkaline denatured protein. The method should be generally applicable to other proteins that contain tyrosines. Analysis of the titration curves suggests that the four tyrosines in native alpha-lactalbumin have pK values of 10.5, 11.8, 11.8, and 12.7, respectively. After the alkaline transconformation, all of them become titrated normally with a pK value of 10.3. A comparison of these results with the ionization behavior of tyrosines in hen egg white and human lysozymes is presented and discussed in terms of differences in the sequences of the proteins.

Animals↗
PubMed1979

Equilibrium and kinetics of the thermal unfolding of yeast 5S ribosomal RNA.

The equilibrium and kinetics of thermal unfolding of yeast 5S ribosomal RNA have been studied by optical methods, in a low ionic strength environment without Mg2+, to follow the disruption of the secondary structure base pairs in the molecule. The equilibrium results demonstrated that all of the helical regions melted simultaneously, and the kinetics of the thermal unfolding were first order. These findings suggest the validity of the two-state approximation for the unfolding reaction under the present conditions. The total number of secondary structure base pairs estimated from our experiment was consistent with that contained in the conformational model based on the Raman spectrum rather than that in the one derived by the enzymic digestion method. Taking our results on the kinetic behavior of the thermal unfolding overall, we propose that the 5S RNA has a partly melted secondary structure under the solvent conditions used.

Circular Dichroism↗
PubMed1978

Detection and characterization of the intermediate on the folding pathway of human alpha-lactalbumin.

To discuss the relation between the folding mechanism and the chemical structure of proteins, the reversible unfolding reactions of human alpha-lactalbumin by acidification and by guanidine hydrochloride at 25 degrees C are studied by means of circular dichroism, difference spectra and pH-jump measurements and are compared with those for bovine alpha-lactalbumin. As shown previously for bovine alpha-lactalbumin, the folding process at neutral pH is not explained by a simple two-state mechanism but involves an intermediate form that has the same amount of helical structures as the native form. The transition between the intermediate and the fully denatured states is too rapid to be measured and corresponds to the helix-coil transition of the backbone. One of the differences of human alpha-lactalbumin from the bovine protein is the remarkable stability of the intermediate at neutral pH, which can be explained by differences in the primary chemical structure. Another difference is the existence at acid pH of an additional helical form, which is more helical than the native form. The transition from this to the intermediate or to the fully denatured one also is shown to resemble the helix-coil transition. The following folding scheme of human alpha-lactalbumin is proposed: formula: (see text). Here N is the native form, and the intermediate is a macroscopic state distributed around the state A3 at neutral pH, while the distribution in the acid and fully denautured states shifts toward Am and A-n, respectively.

Circular Dichroism↗
PubMed1978

Equilibrium and kinetics of the thermal unfolding of alpha-lactalbumin. The relation to its folding mechanism.

The thermal unfolding of alpha-lactalbumin has been studied by equilibrium measurements of aromatic difference spectra, and by kinetic measurements of the Joule heating temperature-jump. The unfolding at neutral pH is a reversible two-state transition. The equilibrium transition curves are analyzed by the nonlinear squares method, which gives correct values of thermodynamic parameters based on the data in a wide range of temperature. The results are discussed in relation to the previous studies on the unfolding by guanidine hydrochloride or by acid. The thermally unfolded state, a partially unfolded species, is shown to be thermodynamically similar to but not identical with the acid state. The folding pathway deduced from the kinetic results is essentially consistent with the folding model of alpha-lactalbumin proposed previously. Large decreases in entropy and in heat capacity during the reversed activation suggest the packing of the folded segments by hydrophobic interactions, while the forward activation shows a marked temperature dependence, probably caused by the disruption of specific long-range interactions.

Chemical Phenomena↗
PubMed1978

Leukemic lymphosarcoma (LLS) with monoclonal IgM: idiotypic specificity on the cell surface and in the cytoplasm of lymphosarcoma cells.

A case of leukemic lymphosarcoma with a small amount of monoclonal IgM in the serum is described. Immunologic investigations showed that about 10% of the abnormal cells formed EAC rosettes, that most of these cells had IgMlambda on the cell surface, and that 40% of them contained IgMlambda in the cytoplasm. Monoclonal IgM was detected in the 19S fraction of the serum despite the lack of monoclonal change as determined by serum electrophoresis or immunoelectrophoresis. The common idiotypic specificity was found in the monoclonal serum IgM, surface Ig, and cytoplasmic Ig of lymphosarcoma cells using antiidiotypic antiserum prepared against purified serum IgM. After chemotherapy, cells with idiotypic determinants disappeared and the serum IgM changed from a monoclonal to a polyclonal distribution.

Adult↗
PubMed1977

Thermodynamic characterization of partially denatured states in the denaturation process of bovine alpha-lactalbumin by inorganic denaturants.

In an attempt to understand the specific effect of inorganic protein denaturants, lithium cation and perchlorate anion, upon the molecular conformation of bovine alpha-lactalbumin and to characterize the denatured states of the protein and the denaturation processes, themodynamic studies on the reversible unfolding of the protein in the presence of lithium chloride, lithium perchlorate and sodium perchlorate were made by means of circular dichroism and ultraviolet absorption measurements. The denaturation reaction caused by lithium chloride was found to take place in a three-state type, while that caused by the two perchlorates in a two-state type. The latter produces the same denatured state as the acid does on the protein, the state where the helical structures remain unchanged. The former produces two kinds of the denatured state, one being a less unfolded state than the acid denatured one and the other a fully unfolded state which is identical with the finally denatured state induced by organic denaturants such as guanidinium chloride, guanidinium thiocyanate and urea.

Animals↗
PubMed1977

Equilibrium and kinetics of the unfolding of alpha-lactalbumin by guanidine hydrochloride (IV): dependence of the N equilibrium A transconformation on the temperature.

The reversible unfolding from the native (N) state to the acid (A) state of alpha-lactalbumin by guanidine-HCl (0.8-2.0 M) was studied at 10-35 degrees C by means of difference spectra and pH-jump measurements. At each temperature, all points plotted as the logarithmic equilibrium constant log KNA of the N equilibrium A process against pH could fall on a curve independent of the denaturant concentration by shifting each point along the log KNA axis, where the shift factor f did not depend on temperature. Moreover, by shifting the points at each temperature along the log (KNA/f) axis, a master curve, independent of both temperature and the denaturant concentration, could be obtained for the pH-dependence of log KNA. From the dependence of the logarithmic rate constants on pH, master curves independent of both temperature and the denaturant concentration could also be made for the N leads to A and the A leads to A processes, where A mean the activated state. The results show the two-state character of the N equilibrium A process. The enthalpy changes and the differences in heat capacity for the N equilibrium A, N equilibrium A and A equilibrium A processes were determined from the accurate measurements of temperature dependence of the unfolding at pH 4.3 and 1.0 M guanidine-HCl. The results show that the disruption of hydrophobic interaction is caused mainly in the A leads to A process, while most of the changes in the pK values of the ionizing groups are caused in the N leads to A process.

Guanidines↗