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Naoki Tanaka

Publications and source records attributed to Naoki Tanaka.

46 records · Page 3Linked to original sources
PubMed2002

The substrate binding domain of DnaK facilitates slow protein refolding.

We examined the effects of a fragment of the substrate binding domain of DnaK on protein refolding from chemically denatured states. The fragment DnaK384-638, containing a full-length substrate binding domain, tightly binds to the unfolded protein in solution. The effects of DnaK384-638 on the reactivation of beta-galactosidase and luciferase were examined at low substrate concentration and low temperature, conditions in which the folding is significantly slow (several days) but the reactivation yield is higher than those in ordinary refolding conditions. In the presence of DnaK384-638, the maximum yield of active beta-galactosidase was improved from 45% to 65% after a 48-h refolding reaction. Spectroscopic experiments showed that DnaK384-638 bound to partially structured monomers of beta-galactosidase and consequently suppressed aggregation. DnaK384-638 accelerated the refolding of luciferase to attain equilibrium in 8 h. On the other hand, DnaK386-561, which has no affinity for the substrate, had no chaperone activity for the reactivation of these proteins. These results indicate that the substrate binding of DnaK384-638 facilitates slow protein refolding.

Binding Sites↗
PubMed2002

Effects of guanidine hydrochloride and high pressure on subsite flexibility of beta-amylase.

We investigated the effects of guanidine hydrochloride (GuHCl) and high pressure on the conformational flexibility of the active site of sweet potato beta-amylase by monitoring the sulfhydryl reaction and the enzymatic activity. The reactivity of Cys345 at the active site, one of six inert half cystine residues of this enzyme, was enhanced by GuHCl at concentrations below 0.5 M. A GuHCl-induced change of the active site was also observed through an intensity change in the near-UV circular dichroism (CD) spectrum. On the other hand, the native conformation of sweet potato beta-amylase observed through fluorescence polarization, far-UV CD spectrum and intrinsic fluorescence was not influenced by GuHCl at concentrations below 0.5 M. Therefore, Cys345 reaction caused by GuHCl was due to an alteration of the local conformation of the active site. GuHCl-induced reaction of Cys345, located in the vicinity of subsites 3 and 4, is attributed to enhanced subsite flexibility, which is responsible for substrate slipping in a single-chain attack mechanism. Due to the flexible conformation, the local region of the subsite is more susceptible to GuHCl perturbation than the molecule overall. The enzymatic activity of sweet potato beta-amylase was reversibly inhibited by GuHCl at concentrations below 0.5 M, and kinetic analysis of the enzymatic mechanism showed that GuHCl decreases the kcat value. High pressure below 400 MPa also inactivated sweet potato beta-amylase with an increase in Cys345 reactivity. These findings indicated that excessively enhanced subsite flexibility reduced the enzymatic activity of sweet potato beta-amylase.

Binding Sites↗
PubMed2002

Cold denaturation of proteins under high pressure.

The advantageous usage of the high pressure technique in studies of cold denaturation of proteins is reviewed, with a brief explanation of the theoretical background of this universal phenomenon. Various experimental results are presented and discussed, explaining the plausible image of the cold denatured state of proteins. In order to understand more clearly this phenomenon and protein structure transition in general, several studies on model polymer systems are also reviewed.

Animals↗
PubMed2002

A case of nephrotic syndrome due to lupus nephritis which was controlled with low-density lipoprotein apheresis.

Our report discusses a 29 year old female patient with nephrotic syndrome due to lupus nephritis, biopsy-proven World Health Organization classification Types IVb and V that was controlled with low-density lipoprotein (LDL) apheresis. She was initially treated with steroid therapy, including methylprednisolone pulse therapy, and the serological activity of her systemic lupus erythematosus was suppressed. However, her nephrotic state, accompanied by severe hyperlipidemia, persisted despite the steroid therapy. Since we could not obtain her consent to administer immunosuppressants such as cyclophosphamide, we tried to treat her using LDL apheresis (LDL-A). We found that her urine protein excretion, hyperlipidemia, hypoalbuminemia, and renal function improved following the initiation of LDL-A. This suggests that LDL-A may be an effective therapy for nephrotic syndrome due to lupus nephritis through short-term amelioration of hyperlipidemia.

Adult↗
PubMed2002

A proteomic analysis of leaf sheaths from rice.

The proteins extracted from the leaf sheaths of rice seedlings were separated by 2-D PAGE, and analyzed by Edman sequencing and mass spectrometry, followed by database searching. Image analysis revealed 352 protein spots on 2-D PAGE after staining with Coomassie Brilliant Blue. The amino acid sequences of 44 of 84 proteins were determined; for 31 of these proteins, a clear function could be assigned, whereas for 12 proteins, no function could be assigned. Forty proteins did not yield amino acid sequence information, because they were N-terminally blocked, or the obtained sequences were too short and/or did not give unambiguous results. Fifty-nine proteins were analyzed by mass spectrometry; all of these proteins were identified by matching to the protein database. The amino acid sequences of 19 of 27 proteins analyzed by mass spectrometry were similar to the results of Edman sequencing. These results suggest that 2-D PAGE combined with Edman sequencing and mass spectrometry analysis can be effectively used to identify plant proteins.

Amino Acid Sequence↗
PubMed2002

Identification of functions of peroxisome proliferator-activated receptor alpha in proximal tubules.

Peroxisome proliferator-activated receptor alpha(PPARalpha) is a member of the steroid/nuclear receptor superfamily that is intensively expressed in the kidney, but its physiologic function is unknown. In this study, PPARalpha-null mice were used to help clarify the function. Starved PPARalpha-null mice were found to secrete significantly more quantities of urine albumin than starved wild-type mice. Furthermore, the appearance of giant lysosomes, marked accumulation of albumin, and an impaired ability concerning albumin digestion were found only in proximal tubules of the starved PPARalpha-null mice. These abnormalities were probably derived from ATP insufficiency as a result of the starvation-induced decline of carbohydrate metabolism and a lack of PPARalpha-dependent fatty acid metabolism. It is interesting that these abnormalities disappeared when glucose was administered. Taken together, these findings demonstrate important functions of PPARalpha in the proximal tubules, the dynamic regulation of the protein-degradation system through maintenance of ATP homeostasis, and emphasize the importance of the fatty acid metabolism in renal physiology.

Adenosine Triphosphate↗
PubMed2002

[The validity of the gait training to prevent falls and fractures in the elderly].

To prevent falls and fractures in the elderly, improvement of their walking ability is considered to be important. In our Fall Prevention program, the walking ability of participants has improved in terms of walking speed and stride length. To perform a quantitative analysis of the gait, we measured the ground reaction force using a force plate and found that there were reductions in the vertical and forward floor reaction force at push off in elderly people over 70 years of age. Therefore, in gait training in the elderly, it is important to strengthen the triceps surae to increase the walking ability, although we must always consider the age of the subject and differences in individual ability. Furthermore, it is important to establish better gait training exercises that correspond to the age-dependent changes of the body.

English Abstract↗
PubMed1999

Estimating the amplitude of measurement noise present in chaotic time series.

We propose a method for estimating the amplitude of measurement noise present in chaotic time series. This method is based on the evaluation of initial errors for a given time series and for a new one synthesized by adding an adequate amount of noise to the given one. The method is valid over a much wider range of noise levels than the previous methods are because it is not based on the detail of dynamical structure which generates the data. In addition, it is possible to check if the method is valid for the given data prior to its application. To confirm the effectiveness of the method we show the results of numerical experiments and apply the method to chaotic data obtained from an electrochemical experiment. (c) 1999 American Institute of Physics.

Journal Article↗
PubMedDate not supplied

Proteome approach to characterize the methylmalonate-semialdehyde dehydrogenase that is regulated by gibberellin.

Proteins regulated by gibberellin (GA) in rice were determined by proteome analysis. Proteins extracted from suspension culture cells of slr1, a constitutive GA response mutant of rice, were separated by two-dimensional polyacrylamide gel electrophoresis, and three proteins were greatly accumulated in the mutant. The most up-regulated protein was methylmalonate-semialdehyde dehydrogenase (MMSDH), and the amount of protein was 7-fold that of wild type. In this study, the function of MMSDH in rice was analyzed. MMSDH gene expression in suspension culture cells, roots, and leaf sheaths ofslr1 was higher than that in its wild-type. MMSDH expression in wild-type roots was increased by exogenous GA(3). Analyzed by in situ hybridization, MMSDH mRNA was expressed in root primordia of slr1, where cells are undergoing growth. MMSDH gene expression in the root zone of tissue differentiation was higher than in the elongation zone or meristem. Transgenic rice expressing antisense MMSDH showed that its seminal roots were thinner than that of control, and that the leaf sheath elongation was slightly inhibited compared to control. Concentrations of TCA cycle metabolites were decreased in the antisense plants as compared with the control plants, suggesting that acetyl-CoA was reduced in the antisense plants. These results suggest that one of the regulations by GA signal transduction including SLR1 is the expression of MMSDH, and that MMSDH may play a role in root development and leaf sheath elongation in rice.

Electrophoresis, Gel, Two-Dimensional↗