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Biomedical subjects

H Tokuda

Publications and source records attributed to H Tokuda.

At least 199 records · Page 11Linked to original sources
PubMed1995

Anti-tumour-promoting glyceroglycolipids from the green alga, Chlorella vulgaris.

Two new monogalactosyl diacylglycerols were isolated from the freshwater green alga, Chlorella vulgaris, as anti-tumour promoters, together with three monogalactosyl diacylglycerols and two digalactosyl diacylglycerols. The new monogalactosyl diacylglycerol containing (7Z,10Z)-hexadecadienoic acid showed a more potent inhibitory effect toward tumour promotion than the other glycerolipids isolated.

Anticarcinogenic Agents↗
PubMed1995

Molecular analysis of elastic properties of the stratum corneum by solid-state 13C-nuclear magnetic resonance spectroscopy.

To elucidate the precise molecular mechanisms underlying stratum corneum (SC) elasticity, we investigated the molecular dynamics of chemical residues within keratin fibers of human plantar SC under various conditions by cross polarization/magic angle spinning 13C-nuclear magnetic resonance. The intensities of nuclear magnetic resonance spectra responsible for amide carbonyl, C alpha methine, and side-chain aliphatic carbons in the intact SC decreased markedly with increasing water content of up to 30% in dry SC, and then remained constant at greater than 30%. Lipid extraction of intact SC with acetone/ether (1:1) did not induce any significant change in the nuclear magnetic resonance spectrum, whereas additional treatment with water, which released natural moisturizing factors (mainly amino acids), caused the SC to lose elasticity. The observed decrease in elasticity of the SC recovered after treatment with basic and neutral amino acids, but not after treatment with acidic amino acid. With the latter treatment, movement of amino acid molecules was significantly disturbed, suggesting a strong interaction with keratin fibers. Parallel studies of the complex elastic modulus of a pig SC sheet with a rheovibron also demonstrated that removal of natural moisturizing factor reduced the elasticity of the SC; this effect was also reversed by the application of basic and neutral amino acids, but not by the application of acidic amino acid. These findings suggest that structural keratin proteins, mainly consisting of 10-nm filaments, acquire their elasticity with the help of hydrated natural moisturizing factor via the reduction of intermolecular forces, probably through nonhelical regions between keratin fibers.

Amino Acids↗
PubMed1995

Inhibitory effect of natural carotenoids on Epstein-Barr virus activation activity of a tumor promoter in Raji cells. A screening study for anti-tumor promoters.

As a screening study for anti-tumor promoters, 51 carotenoids with diverse structures were examined for their inhibitory effects on the Epstein-Barr virus activation activity of 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. The results showed that most of the carotenoids exhibited inhibitory activity, and in general, no cytotoxicity on Raji cells was observed in the assay. Among the carotenoids, beta-cryptoxanthin, lutein, and lactucaxanthin showed the strongest inhibitory activity, superior to the well known anti-tumor promoter, beta-carotene. Heteroxanthin, peridinin, and halocynthiaxanthin showed cytotoxicity at the high concentration (1000 molar ratio per TPA), but indicated a strong inhibitory effect at the lower concentrations, which were only weakly toxic (500 and 100 molar ratios). Based on these results, the essential moiety for the activity of carotenoids was considered to be the 3-hydroxy-epsilon-end group.

Antineoplastic Agents, Phytogenic↗
PubMed1995

Inhibitory effects of cucurbitane triterpenoids on Epstein-Barr virus activation and two-stage carcinogenesis of skin tumor. II.

To search for possible anti-tumor-promoters, we carried out a primary screening of twenty-four 29-nor-cucurbitacin glucosides isolated from the roots of Cayaponia tayuya (Cucurbitaceae) using an in vitro synergistic assay system. Of these glucosides, cayaponosides B (5), B3 (7), D (8), D3b (22) and C2 (23) exhibited significant inhibitory effects on Epstein-Barr virus (EBV) activation induced by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA). Furthermore, 5 and 23 exhibited remarkable anti-tumor-promoting effects on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test.

Animals↗
PubMed1995

Inhibitors of skin-tumor promotion. XIII. Inhibitory effects of euglobals and their related compounds on Epstein-Barr virus activation and on two-stage carcinogenesis of mouse skin tumors. (2).

One hundred and fifteen synthesized mono, di, and trihydroxybenzamide and thiobenzamide derivatives having structures related to euglobals were examined for their inhibitory effects on Epstein-Barr virus (EBV) activation by 12-O-tetradecanoylphorbol-13-acetate (TPA) as a primary screening test for anti-tumor-promoters. In general, 3-acyl-2,4,6-trihydroxybenzamide and 3-acyl-2,4,6-trihydroxythiobenzamide derivatives exhibited strong or moderate activities, and the latter compounds were less cytotoxic than the former. Meanwhile, little or no activity was observed with mono and dihydroxybenzamide and dihydroxythiobenzamide derivatives. Structural requirements for the activities of these compounds have been discussed in detail. Among the above compounds, compounds 36 and 73, which were significantly active on the inhibition of EBV activation, were investigated using a two-stage mouse skin carcinogenesis test induced by 7,12-dimethylbenz[a]anthracene (DMBA) and TPA. The results of the in vivo test showed that both compounds have a stronger inhibitory effect than that of the well-known anti-tumor-promoter, glycyrrhetic acid. These results suggested that the two compounds might be valuable as anti-tumor-promoters in chemical carcinogenesis.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1995

Anti-tumor-promoting activities of euglobals from Eucalyptus plants.

To search for possible anti-tumor-promoters (chemopreventive agents), we carried out a primary screening of 21 euglobals (acylphloroglucinol-monoterpene or -sesquiterpene structures) isolated from the juvenile leaves of five species of Eucalyptus plants using an in vitro synergistic assay system. Of these compounds, euglobal-G1--G5 (1-5), -Am-2 (15) and -III (16) exhibited significant inhibitory effects on Epstein-Barr virus (EBV) activation induced by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA). Furthermore, the effects of compounds 1 and 16 on the cell cycle of Raji cells were also examined by a flow cytometer, and both compounds 1 and 16 exhibited strong inhibition on the effect of the cell cycle induced by TPA. These two euglobals (1 and 16) exhibited remarkable anti-tumor-promoting effects on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1995

Application of direct current to protect bioreactor against contamination.

Bacteria cell suspensions were sterilized by direct electric current and the cell death rate was proportional to the current. When repeated hydrolysis of casein by immobilized mycelia was done under 0.06 A of direct electric current, contaminants were inhibited while the hydrolysis was stable for more than 10 batches (250 h).

Bacteria↗
PubMed1995

[A case of primary pulmonary non-Hodgkin's lymphoma showing a fine granular pattern around the main tumor on thin-slice CT].

A 61-year-old woman was admitted for evaluation of an abnormal shadow found incidentally on a chest radiograph. A 35 x 20 mm nodule with an ill-defined margin was found at the left hilum on conventional CT. Thin-slice (2 mm) CT was done, and a fine granular zone was found around the lesion. Left upper lobectomy was done and the lesion proved to be a primary pulmonary non-Hodgkin's lymphoma (small cell type, B-cell). The granular pattern seen on CT was found to correspond to intraseptal micronodules scattered along the lymphatic vessels, a finding which is considered to be pathognomonic of pulmonary lymphomas by many pathologists. We know of no previous description of how these histologic characteristics can appear on high-resolution thin-slice CT. These findings will be helpful for the CT diagnosis of pulmonary lymphoma.

Diagnosis, Differential↗
PubMed1994

Glucocorticoid inhibits cAMP production induced by vasoactive agents in aortic smooth muscle cells.

It is well-known that atherosclerotic change and hypertension are common manifestations in patients with glucocorticoid excess. We previously reported that pituitary adenylate cyclase activating polypeptide (PACAP), prostaglandin E2 (PGE2) and carbacyclin, a stable analog of prostacyclin, have suppressive effects on vasopressin-induced DNA synthesis of rat aortic smooth muscle cells through cAMP production (Murase et al., J. Hypertens., 10 (1992) 1505; Oiso et al., Biochem. Cell. Biol., 71 (1993) 156). In the present study, we investigated the effect of glucocorticoid on cAMP production induced by PACAP, PGE2 and carbacyclin in aortic smooth muscle cells. The pretreatment with dexamethasone significantly inhibited cAMP accumulation induced by these vasoactive agents in a dose dependent manner in the range between 10 pM and 10 nM. These inhibitory effects of dexamethasone were dependent on the time of pretreatment up to 8 h. Dexamethasone inhibited cAMP accumulation induced by NaF, a GTP-binding protein activator, and forskolin which directly activates adenylate cyclase. Moreover, forskolin-induced adenylate cyclase activity was significantly reduced in membranes prepared from the cells treated with dexamethasone. These results strongly suggest that glucocorticoid inhibits cAMP production induced by vasoactive agents in primary cultured rat aortic smooth muscle cells and the inhibitory effect is exerted at the level of adenylate cyclase.

Animals↗
PubMed1994

Reconstitution of an efficient protein translocation machinery comprising SecA and the three membrane proteins, SecY, SecE, and SecG (p12).

A cytoplasmic membrane protein, p12, of Escherichia coli was discovered as a new factor that stimulates the protein translocation activity reconstituted with SecA, SecY, and SecE (Nishiyama, K., Mizushima, S., and Tokuda, H. (1993) EMBO J. 12, 3409-3415). Direct involvement of p12 in protein translocation was subsequently demonstrated in vivo by genetic studies, and the name SecG has been proposed for p12 (Nishiyama, K., Hanada, M., and Tokuda, H. (1994) EMBO J. 13, 3272-3277). To elucidate the role of SecG in protein translocation and to characterize the translocation apparatus comprising these four Sec proteins, the activity of reconstituted proteoliposomes was examined in detail as a function of the amount of each component. SecG markedly stimulated the translocation activity over wide ranges of amounts of the other three Sec proteins, indicating that none of the other three Sec proteins substitutes for the SecG function. Detailed kinetic analyses indicated that the activity of proteoliposomes was dependent on the amount of the SecY-SecE complex when SecG was absent and the amount of the SecY.SecE.SecG complex when the proteoliposomes contained SecG. The translocation activity of the latter complex was significantly higher than that of the former one. Binding of SecA to liposomes appreciably increased when they contained both SecY and SecE, whereas the further presence of SecG did not enhance the binding. On the other hand, the ATPase activity of SecA, which was dependent on proOmpA and SecY.SecE-containing proteoliposomes, was significantly enhanced when the proteoliposomes contained SecG. Taken together, these results indicate that SecG enhances the translocation activity of the apparatus after the step of SecA targeting to SecY.SecE.

Adenosine Triphosphatases↗
PubMed1994

Band 1 subunit of Escherichia coli preportein translocase and integral membrane export factor P12 are the same protein.

Escherichia coli preprotein translocase consists of the peripheral membrane protein SecA and the integral membrane domain SecY/E. SecY/E, whether isolated chromatographically or by immunoprecipitation, was found to be complex of three polypeptides, SecY, SecE, and band 1. Band 1 did not correspond to a known sec gene product. The independent purification of the separate integral membrane polypeptides needed for reconstitution of translocation yielded SecY, SecE, and a protein that we termed P12. Based on the sequence of P12, we have prepared antisera to a carboxyl-terminal peptide domain and shown that this antiserum specifically labels only P12 on immunoblots of inner membrane vesicles. We now report that affinity-purified anti-P12 antibodies specifically label the band 1 subunit of the SecY/E complex, whether the SecY/E was isolated chromatographically or by precipitation with antibodies to an epitope-tagged SecY subunit. In addition, the antiserum to P12 can specifically immunoprecipitate the full three-subunit SecY/E complex from detergent extracts. This finding completes the identification of the polypeptides that are essential for catalysis of preprotein translocation.

Adenosine Triphosphatases↗
PubMed1994

Disruption of the gene encoding p12 (SecG) reveals the direct involvement and important function of SecG in the protein translocation of Escherichia coli at low temperature.

The Escherichia coli cytoplasmic membrane protein, p12, stimulates the protein translocation activity reconstituted with SecY, SecE and SecA. The gene encoding p12, which is located at 69 min on the E. coli chromosome, was deleted to examine the role of p12 in protein translocation in vivo. The deletion strain exhibited cold-sensitive growth. Pulse-chase experiments revealed that precursors of outer membrane protein A, maltose binding protein and beta-lactamase accumulated at 20 degrees C but not at 37 degrees C. The deletion strain harboring a plasmid which carries the gene encoding p12 under the control of the araBAD promoter was able to grow in the cold when p12 was expressed with the addition of arabinose. Furthermore, the accumulated precursors were rapidly processed to the mature forms upon the expression of p12. Immunoblot analysis revealed the steady-state accumulation of precursor proteins at 20 degrees C, whereas the accumulation was only marginal at 37 degrees C, indicating that the function of p12 is more critical at 20 degrees C than at 37 degrees C. Finally, proteoliposomes were reconstituted with or without p12 to demonstrate that the stimulation of the activity by p12 increases with a decrease in temperature. From these results, we concluded that p12 is directly involved in protein translocation in E. coli and plays a critical role in the cold. We propose the more systematic name, SecG, for p12.

ATP-Binding Cassette Transporters↗
PubMed1994

Biochemical characterization of the presecretory protein translocation machinery of Escherichia coli.

The protein translocation apparatus in Escherichia coli has been studied both genetically and biochemically. In vitro protein translocation systems involving everted membrane vesicles or reconstituted proteoliposomes have significantly contributed to biochemical clarification of the structure, mechanism and energetics of the apparatus. It is established that SecA, SecY and SecE are essential components, and play fundamental roles in the translocation reaction, and that both ATP and a proton motive force are required for the translocation. A new membrane factor, SecG, was found to participate in the formation of the apparatus, causing significant enhancement of the activity. SecD was found to play a role in the release of translocated proteins from the outer surface of the cytoplasmic membrane.

Adenosine Triphosphatases↗
PubMed1994

Orientational and aggregational states of magainin 2 in phospholipid bilayers.

Magainins from Xenopus skin are antimicrobial peptides with broad spectra, and their action mechanisms are considered to be the permeabilization of bacterial membranes. To elucidate their molecular mechanisms, three analog peptides of magainin 2, each having a Trp residue substituted for Phe at the 5th, 12th, or 16th position, were synthesized, and their interactions with acidic phospholipid membranes were investigated by fluorescence. The Trp substitution did not significantly affect the properties of the parent peptide. The binding isotherms of these peptides to the membranes, which were obtained on the basis of fluorescence changes upon membrane binding of the peptides, were sigmoidal, suggesting the association of the bound peptide molecules. A quantitative analysis indicated that the formed aggregate is a dimer. The observation that the initial rate constant of magainin 2 induced leakage of calcein from liposomes was dependent on the fourth power of the peptide concentration demonstrates the formation of a tetrameric pore. A blue shift and intensity enhancement of Trp fluorescence in the presence of the membranes indicate that those Trp residues are buried in the hydrophobic region of the bilayers. Furthermore, the depths of the Trp residues, which were determined using the n-doxylphosphatidylcholine quenching technique, were about 10 A from the bilayer center irrespective of the peptide aggregational state. Thus, it was concluded that the orientation of the magainin 2 alpha-helix is parallel to the membrane surface. A model of the pore formation will be proposed on the basis of these observations.

Amino Acid Sequence↗