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S Sugai

Publications and source records attributed to S Sugai.

At least 217 records · Page 12Linked to original sources
PubMed1983

Melting of local ordered structures in yeast 5S ribosomal RNA in aqueous salts.

Equilibrium and kinetics of thermal melting of yeast 5S ribosomal RNA in aqueous NaCl with or without Mg2+ were investigated by differential thermal melting and temperature jump methods. Two peaks (1 and 2) and a shoulder were observed in each of melting curves at ionic strength I=0.002-0.5 and linearity between each of melting temperatures T1m and T2m and log I was found at I=0.01-0.5 in the Mg2+-free solution. The local structures were found to be stabilized considerably by Mg2+. The temperature jump measurements gave the kinetic melting curve of the structure 1 at I=0.03 without Mg2+ or with 0.5 mM Mg2+. The kinetic Tm coincided well with the corresponding static Tm. For the structure 1, various parameters were calculated from the kinetic data, which indicated a double helical character of the structure 1. In terms of the values of Tm, G-C content, and enthalpy change of the transition of the structure 1 or 2, appropriateness of each of the secondary structure models of eukaryotic 5S RNA proposed previously was discussed.

Hot Temperature↗
PubMed1983

Interactions of divalent metal ions with bovine, human, and goat alpha-lactalbumins.

Bovine, human, and goat alpha-lactalbumins prepared by the ordinary methods were found to contain 1.1-1.3 atoms of Ca per protein molecule. Removal of Ca2+ was shown to destabilize the tertiary structures in the three proteins. The three apoproteins were indicated to change in the conformation by heat from the native-like to the unfolded state. Degree of restoration of the native tertiary structure in 5 mM Tris-HCl and 0.1 mM EDTA at pH 7.2 and 25 degrees C by addition of Ca2+ was determined from change in CD ellipticity at 270 nm, and the apparent binding constant of Ca2+ was analyzed to be 2.5 X 10(8) (bovine), 3.0 X 10(8) (human), and 2.8 X 10(8) M-1 (goat). Also, value of the binding constant of Ca2+ to the native-like apoform was estimated from the apparent binding constant and equilibrium constant of the conformational change of the apoform. The binding properties of Mn2+, Mg2+, and Zn2+ to the bovine protein at neutral pH are also discussed.

Animals↗
PubMed1983

B-cell malignancy and monoclonal gammopathy, and idiotype of cell surface and serum immunoglobulin.

We studied cell surface membrane immunoglobulins (SmIg), intracytoplasmic Ig (CIg) and monoclonal Ig (M protein) in patients with the B-cell series malignancies; malignant lymphoma, chronic lymphocytic leukemia (CLL), Waldenström's macroglobulinemia (WM), multiple myeloma (MM), and monoclonal gammopathy (MG) associated with Sjögren's syndrome (SS). The patients were examined for idyotype (Id) determinants on the cell surface and in the cytoplasm of malignant cells as well as serum M proteins. Twenty-two patients had malignant lymphoma with monoclonal SmIg. The malignant cells of 11 patients contained CIg; four of these 11 patients had a small amount of serum M protein. SmIg of the IgM class was most frequent (12/22) and the lambda type light chain was predominant (kappa/lambda ratio = 4/8). By means of rabbit anti-Id antisera prepared against M proteins, Id determinants were demonstrated on the cell surface and in the cytoplasm of malignant cells as well as in the serum M proteins, indicating that the malignant cells proliferated monoclonally producing monoclonal IgM on the cell surface and in the cytoplasm and secreting it to the serum. Six CLL patients were included in our series; one manifested monoclonal IgM in the serum. The Id determinants of M protein was detected on the cell surface and in the cytoplasm of pathologic cells in the peripheral blood. Eight of ten WM patients were examined for SmIg; all had monoclonal SmIg on the surface of cells from peripheral blood or bone marrow. Id determinants were detected on the cell surface and in the cytoplasm of malignant cells in four WM patients. There were 42 patients with MM; 10 of them were examined for SmIg and three of these had monoclonal SmIg on plasma cells derived from the bone marrow. By immunofluorescent and mixed rosette methods, Id-bearing B (0-20%) and T cells (0-2%) were identified in the peripheral blood of MM patients who had no plasma cells in the peripheral blood. Our findings suggest that a monoclonal change may occur at the B-cell level and that Id-bearing T cells may exist as regulatory T cells. Ten SS patients had M proteins. Non-IgM class M proteins (2 IgG and 4 IgA) were more frequent than the IgM class (3 IgM). Four M proteins with rheumatoid factor (RF) activity were found among these 10 M proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1981

Kinetic correlations between the disulfide bond reduction and the induced conformational change of proteins.

Kinetic correlations between the disulfide bond reduction in excess dithioerythritol and the induced conformational change were studied on two proteins, bovine alpha-lactalbumin and soybean trypsin inhibitor, at 25 degrees C and pH 8.0-8.5 by measuring the absorbance of oxidized dithioerythritol at 310 nm and the ellipticity at 270 nm, respectively. With alpha-lactalbumin, in the absence of guanidine hydrochloride (Gdn x HCl) or in dilute Gdn x HCl, the kinetics for the bond reduction and the conformational change were both of a biphasic type. The fast phase was complete within a few seconds and was associated with the reduction of some of the disulfide bonds and with almost complete loss of the tertiary structure. The slow phase was associated with the reduction of other disulfide bonds. In concentrated Gdn x HCl, the kinetics of both processes were observed as a single phase, the rate of which was similar to that of the slow phase in the absence of Gdn x HCl or in dilute Gdn x HCl. In all cases studied, the rate of the bond reduction was similar to that of the conformational change induced. By correcting the change in absorbance at 310 nm to a contribution from the protein due to the conformational change, the number of bonds which are reduced in the fast phase in the absence of Gdn x HCl was determined to be 1.0-1.1. It was shown, taking observations of others and theoretical results into account, that the bond reduced in the fast phase might be the one between Cys 6 and Cys 120. On the other hand, on of two bonds of soybean trypsin inhibitor in the native form was reduced in the fast phase without any loss of the tertiary structure, and the other was reduced in the slow phase. Considering the results of other researchers, it was concluded that the bond reduced in the fast phase of the inhibitor is a 136-145 bond.

Animals↗
PubMed1981

Role of the interaction between ionizable groups in the folding of bovine alpha-lactalbumin.

Previous studies of the reversible unfolding of alpha-lactalbumin in the acid to neutral pH region have shown that the unfolding transition with guanidine hydrochloride involves a stable intermediate which is similar to a partially unfolded state produced by acid transition. In order to clarify how the interaction of ionizable groups takes part in stabilization of the native structure during the folding of the protein, the transitions were further investigated in the alkaline region in the presence of the denaturant by means of circular dichroism, difference spectra and pH-jump measurements, and the effects of pH on the equilibrium and kinetics of the unfolding in the whole pH region are discussed. The alkaline state is indistinguishable from the acid state in equilibrium and kinetic properties. Thus, as a first approximation, the total unfolding in the whole pH region can be expressed as a three-state mechanism involving the native (N), the intermediate (A), and the fully unfolded (D) states. The strong pH dependence of the N Equilibrium A transition above pH 10 is almost entirely ascribable to the abnormal tyrosines in the N state previously detected by the pH-jump titration method, while the dependence between pH 7 and 10 also suggests the presence of an abnormal alpha-amino group. The normalization of most of the alkaline and the acidic abnormally ionizable groups in the N state occurs simultaneously in the first step of the unfolding pathway, i.e., the forward activation of the N Equilibrium A transition, and the final step of the folding may be associated with the interaction of the ionizable groups. Among the abnormally ionizable groups detected, the tyrosyl and carboxyl groups are most important in view of the large changes in their pK values, suggesting the presence of some interactions, even if only indirect, between these groups. Alignment data of amino acid residues also suggest that at least one such abnormal tyrosyl residue (Tyr 50) and its neighbors are conserved throughout in the alpha-lactalbumin-lysozyme group of proteins. Possible mechanisms of the interaction between the tyrosyl and carboxyl groups are discussed.

Animals↗