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T Higuchi

Publications and source records attributed to T Higuchi.

At least 37 records · Page 2Linked to original sources
PubMed1992

Three stages of copper accumulation in hepatocellular lysosomes: X-ray microanalysis of copper-loaded golden hamsters.

Male golden hamsters were loaded with copper by supplying them for up to 12 weeks with drinking water containing 0.5% cupric acetate. The copper feeding increased hepatic copper to widely varying levels. Energy dispersive X-ray microanalysis could always identify a copper-sulphur complex in the hepatocyte lysosomes of copper-loaded hamsters and the X-ray intensity of copper was found to be a reliable parameter to measure in-situ copper accumulation. Combining this parameter with the copper binding ratio expressed by delta Cu/delta S enabled us to discern two stages of sub-histochemical copper accumulation. The first stage was marked by low levels of both lysosomal copper and binding ratio, which suggested that this initial copper transfer was mediated by unsaturated cuproproteins. The second stage was characterized by median amounts of lysosomal copper and a binding ratio of more than 0.50. At the third stage, histochemically detectable copper appeared in animals whose lysosomal copper was extraordinarily high in later experimental periods. With the copper binding ratio being in the same range of 0.50-0.83, it seemed that saturated cuproproteins were the main mediator of copper transport in the later two stages.

Animals↗
PubMed1991

Site-directed mutagenesis of Escherichia coli aspartate aminotransferase: role of Tyr70 in the catalytic processes.

Site-directed mutagenesis of Tyr70 in the active site of Escherichia coli aspartate aminotransferase (AspAT) followed by kinetic studies has elucidated the roles of the hydroxyl group and benzene ring of Tyr70. X-ray crystallographic analysis showed that replacement of Tyr70 by Phe did not alter the active-site conformation of the enzyme. Comparison of the kinetic parameters of the four half-transamination reactions (the pyridoxal 5'-phosphate form of the enzyme with L-aspartate or L-glutamate and the pyridoxamine 5'-phosphate form with oxalacetate or 2-oxoglutarate) between the wild-type and [Tyr70----Phe]AspATs showed that the mutation increases the energy level of the transition state by 2 kcal.mol-1 for all the four substrates, suggesting some contribution of the hydroxyl group of Tyr70 to the transition state. When Phe70 was further replaced by Ser, the energy level of the transition state for L-glutamate or 2-oxoglutarate, but not for L-aspartate or oxalacetate, was further increased by 2-3 kcal.mol-1, suggesting that the presence of a benzene ring at position 70 is essential for recognizing the L-glutamate-2-oxoglutarate pair as substrates.

Amino Acid Sequence↗
PubMed1991

Enhancement by retinoic acid and dibutyryl cyclic adenosine 3':5'-monophosphate of the differentiation and gene expression of human neuroblastoma cells induced by interferon.

Human neuroblastoma cell lines are induced to differentiate and display neuronal phenotypes when treated with interferon (IFN)-alpha 2, retinoic acid (RA), or dibutyryl cyclic AMP (dbcAMP). We investigated the effects of combinations of these agents in induction-differentiation in the neuroblastoma cell line, NUB-6. The inductive effect of IFN-alpha 2 was markedly enhanced when used in combination with RA or dbcAMP. In parallel, RA or dbcAMP also enhanced the level of 2'-5'-oligoadenylate (2-5A) synthetase, and enzyme induced by IFNs and implicated in their biological action. The levels of another IFN-inducible enzyme, p68 kinase, were not enhanced by the combination treatments. The enhancement effects appeared to be exerted largely at the posttranscriptional level as both RA and dbcAMP stabilized IFN-induced 2-5A synthetase mRNA, resulting in increased enzyme activity. Thus, the 2-5A synthetase system is likely involved in mediating the IFN-alpha 2-induced differentiation of neuroblastoma cells and may also mediate the enhancement effects of RA and dbcAMP on IFN activity in these cells. These results also provide a rational basis for establishing a combination therapeutic approach for the treatment of neuroblastoma.

2',5'-Oligoadenylate Synthetase↗
PubMed1991

Thermostable aspartate aminotransferase from a thermophilic Bacillus species. Gene cloning, sequence determination, and preliminary x-ray characterization.

The gene encoding aspartate aminotransferase of a thermophilic Bacillus species, YM-2, has been cloned and expressed efficiently in Escherichia coli. The primary structure of the enzyme was deduced from nucleotide sequences of the gene and confirmed mostly by amino acid sequences of tryptic peptides. The gene consists of 1,176 base pairs encoding a protein of 392 amino acid residues; the molecular mass of the enzyme subunit is estimated to be 42,661 daltons. The active site lysyl residue that binds the coenzyme, pyridoxal phosphate, was identified as Lys-239. Comparison of the amino acid sequence with those of aspartate aminotransferases from other organisms revealed very low overall similarities (13-14%) except for the sequence of the extremely thermostable enzyme from Sulfolobus solfataricus (34%). Several amino acid residues conserved in all the compared sequences include those that have been reported to participate in binding of the coenzyme in three-dimensional structures of the vertebrate and E. coli enzymes. However, the strictly conserved arginyl residue that is essential for binding of the distal carboxyl group of substrates is not found in the corresponding region of the sequences of the thermostable enzymes from the Bacillus species and S. solfataricus. The Bacillus aspartate aminotransferase has been purified from the E. coli clone cell extracts on a large scale and crystallized in the buffered ammonium sulfate solution by the hanging drop method. The crystals are monoclinic with unit cell dimensions a = 121.2 A, b = 110.5 A, c = 81.8 A, and beta = 97.6 degrees, belonging to space group C2, and contain two molecules in the asymmetric unit. The crystals of the enzyme-alpha-methylaspartate complex are isomorphous with those without the substrate analog.

Amino Acid Sequence↗
PubMed1991

Tracheo-bronchitis as a complication of Crohn's disease--a case report.

A case of Crohn's enterocolitis associated with diffuse tracheo-bronchitis is presented herein. Although respiratory tract involvement in Crohn's disease is extremely rare, our review of the world literature revealed several common clinical pathologic features. These features include a productive cough with chest X-ray films which are normal except for some peripheral involvement. Bronchoscopy, however, shows diffuse inflammation of the trachea and bronchi with widely scattered whitish lesions while biopsy reveals a granulomatous infiltration of inflammatory cells. This tracheobronchitis typically responds well to treatment with prednisone.

Adult↗
PubMed1991

Multi-center study of seasonal affective disorders in Japan. A preliminary report.

A multi-center study on seasonal affective disorder (SAD) was conducted from the autumn of 1988 to the spring of 1989 with the cooperation of 16 facilities in Japan. Forty-six SAD patients were identified among 1104 respondents to our advertisements in mass media, or patients seen at the outpatient clinics. Essentially similar findings to other previous reports were obtained in terms of onset age of the first episode, duration of episode, high proportion of depression in first-degree relatives and atypical vegetative symptoms. However, a nearly equal sex ratio, together with a high proportion of unipolar depression, is characteristic of the present study. Increased appetite and carbohydrate craving were predominant only in female patients, whereas hypersomnia was prominent in both sexes. Effective response to light therapy was found in 17 SAD patients. However, a controlled study on a large number of patients is required to allow final conclusions on the efficacy of light therapy in Japanese SAD patients.

Adolescent↗
PubMed1991

Tyr225 in aspartate aminotransferase: contribution of the hydrogen bond between Tyr225 and coenzyme to the catalytic reaction.

Tyr225 in the active site of Escherichia coli aspartate aminotransferase (AspAT) was replaced by phenylalanine or arginine by site-directed mutagenesis. X-ray crystallographic analysis of Y225F AspAT showed that the benzene ring of Phe225 was situated at the same position as the phenol ring of Tyr225 in wild-type AspAT. The mutations resulted in a great decrease in the rate of the transamination reaction, suggesting that Tyr225 is important for efficient catalysis. The kinetic analysis of half-transamination reactions of Y225F AspAT with four substrates (aspartate, glutamate, oxalacetate, and 2-oxoglutarate) and some analogues (2-methylaspartate, succinate, and glutarate) revealed a considerable increase in the affinities for all these compounds. In contrast, affinity for the amino acid substrates was decreased by mutation to arginine, but affinities for the keto acid substrates and the two dicarboxylates (succinate and glutarate) were increased. The electrostatic interaction between O(3') of the coenzyme [pyridoxal 5'-phosphate (PLP)] and the residue at position 225 affected the pKa value of the Schiff base, which is formed between the epsilon-amino group of Lys258 and the aldehyde group of PLP; based on the spectrophotometric titration the pKa values were determined to be 6.8 for wild-type AspAT, 8.5 for Y225F AspAT, and 6.1 for Y225R AspAT in the absence of substrate. The absorption spectra of the three AspATs were almost identical in the acidic pH region, but the spectrum of Y225F AspAT differed from that of wild-type or Y225R AspAT in the alkaline pH region.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Relation between body size and bone mineral density with special reference to sex hormones and calcium regulating hormones in elderly females.

We studied the relation between body size and bone mineral density in elderly females. The study included a total of 93 ambulatory females aged over 60 years. They were divided into 3 groups according to their body mass index (BMI; kg/m2): slender group with BMI less than 20 (n = 28), normal group with BMI of 20 to 24.9 (n = 43) and obese group with BMI greater than or equal to 25 (n = 22). Fracture incidence, bone mineral density, calcium regulating hormones and steroid hormones were studied in an intergroup comparative manner. The incidence of vertebral fracture was found to be negatively correlated with BMI (the incidences of vertebral fracture in slender, normal and obese were 78.6, 48.8 and 22.7%, respectively) and bone mineral density was also BMI-related (0.390 +/- 0.016, 0.456 +/- 0.015 and 0.493 +/- 0.018 g/cm2, respectively: p less than 0.01 in ANOVA; mean +/- SE). The number of years after menopause was shorter in patients with a higher BMI. There was no intergroup difference in serum levels of PTH, vitamin D and estrogens. On the other hand, serum levels of calcitonin, DHEA, DHEAS, delta-4 androstenedione and testosterone were found to be higher in subjects with a higher BMI. From the present results, it seems that bone mineral density is supported not only by weight-bearing stress upon bone, but also by serum levels of calcitonin and androgens in obese females.

Age Factors↗
PubMed1991

Postnatal development of acetohexamide reductase activities in microsomes and cytosol of rat liver.

The postnatal development of acetohexamide reductase activities in liver microsomes and cytosol were examined in male rats. The developmental pattern of acetohexamide reductase activity in liver microsomes was distinguished from that in liver cytosol. Furthermore, acetohexamide reductase activity in liver microsomes was effectively suppressed by castration, but the activity in liver cytosol was not affected by castration. These results clearly indicate that enzymes with physiologically different roles can catalyze the metabolic reduction of acetohexamide in rat liver.

Age Factors↗
PubMed1991

[The application of in vivo diffusion weighted magnetic resonance imaging to intracranial disorders].

We have developed a magnetic resonance (MR) spin echo method to obtain diffusion weighted imaging using motion-probing gradient (MPG) pulses in one or three orthogonal directions before and after a 180 degree pulse. Phantom models containing water and acetone, normal volunteers and patients with brain tumors, brain edema and infarction were examined. Experimental models of brain edema including triethyltin intoxication and cold injuries were also examined in Wistar rats. MRI was performed at a 1.0-T clinical machine or a 4.7-T experimental machine using spin echo pulse sequences with or without additional MPGs on one or three orthogonal axes. The one direction method was useful to define diffusion anisotropy of myelinated axonal fibers in white matter. Faster diffusion was detected in the white matter parallel to the direction of MPGs. On the other hand, slower diffusion was detected perpendicular to the direction of MPGs because the myelin sheath restricted water diffusion. The three orthogonal gradients method was useful to demonstrate the difference in the diffusion coefficients in various diseases due to its larger total gradient strength. The clear distinction between the cytotoxic edema, which revealed slower diffusion, and the vasogenic edema, which revealed faster diffusion, was demonstrated in the experimental models using diffusion weighted image. In the clinical cases, faster diffusion was demonstrated in the brain tumor and perifocal vasogenic edema, which was in agreement with the results in the experimental models of rats. Brain tumors such as low grade astrocytoma with microcysts and perifocal vasogenic edema have very wide extracellular space.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Reactivity for prostaglandins and inhibition by nonsteridal anti-inflammatory drugs of rabbit liver befunolol reductase.

Befunolol (BF) reductase with 3 alpha-hydroxysteroid dehydrogenase activity, which was purified from rabbit liver, catalyzed the oxidoreduction of prostaglandins, indicating that this enzyme has broad substrate specificities for endogenous substances. BF reductase was strongly inhibited by a variety of nonsteridal anti-inflammatory drugs and then a significant correlation was observed between the logarithms of IC50 (concentration required to produce 50% inhibition of BF reductase activity) values and the maximal daily human doses for nonsteroidal anti-inflammatory drugs. These results suggest that the pharmacological potency of nonsteroidal anti-inflammatory drugs may be predicted from the degree of inhibition of BF reductase by these drugs.

Alcohol Oxidoreductases↗
PubMed1990

Activation of supraoptic neurosecretory cells by osmotic stimulation of the median preoptic nucleus.

In urethane-anesthetized male rats extracellular recordings were obtained from neurosecretory cells in the supraoptic nucleus (SON) while each of electrical stimulation and local osmotic stimulation produced by pressure injection of hypertonic saline was applied to the median preoptic nucleus (MnPO) or to the medial septal nucleus (MS). Electrical stimulation of the MnPO produced orthodromic excitation or initial inhibition followed by strong excitation in most SON cells (59/61), and local osmotic stimulation of the MnPO excited majority of cells (39/51). On the contrary, local osmotic stimulation of the MS did not excite SON cells, although electrical stimulation excited all the cells (5/5). The results suggest that the MnPO is one of the osmosensitive sites controlling electrical activity of SON neurosecretory cells.

Action Potentials↗
PubMed1990

A novel enzymatic decarboxylation of oxalic acid by the lignin peroxidase system of white-rot fungus Phanerochaete chrysosporium.

Oxidation of veratryl alcohol by lignin peroxidase (LiP) was potently inhibited by oxalic acid. The inhibition analysis with Lineweaver-Burk plots clearly showed that the type of inhibition is non-competitive. The enzymatic oxidation of veratryl alcohol in the presence of 14C-oxalic acid yielded radioactive carbon dioxide. The results indicate that the apparent inhibition of LiP is caused by reduction of the veratryl alcohol cation radical intermediate back to the substrate level by oxalate, which is concomitantly oxidized to carbon dioxide.

Benzyl Alcohols↗
PubMed1990

3-Hydroxycoumarins: first direct preparation from coumarins using a Cu2(+)-ascorbic acid-O2 system, and their potent bioactivities.

First direct 3-hydroxylation of a coumarin ring via a purely chemical system, previously only possible using cytochrome P-450, was successfully conducted by a Cu2(+)-ascorbic acid-O2 system; the two 3-hydroxycoumarins obtained were novel compounds, 3-hydroxyscopoletin and 3-hydroxyisoscopoletin. 5-Lipoxygenase and alpha-D-glucosidase inhibitory activities of coumarins greatly increased through 3-hydroxylation. 3-Hydroxyscopoletin and 3-hydroxyumbelliferone had a high inhibitory potency for 5-lipoxygenase and for alpha-D-glucosidase respectively; they serve as lead compounds for new drugs.

Arachidonate 5-Lipoxygenase↗