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Biomedical subjects

M Ariyoshi

Publications and source records attributed to M Ariyoshi.

At least 37 records · Page 2Linked to original sources
PubMed1997

Hemarthrosis of the knee and bone contusion.

We present five patients with acute traumatic hemarthrosis of the knee who also had hemorrhage within the bone marrow around the knee detected by magnetic resonance imaging. No additional bony, ligamentous, meniscal or osteochondral injuries were evident from clinical examination, initial and repeated plain radiographs, or magnetic resonance imaging. The main symptoms were sharply localized pain and tenderness of the contused area. When hemarthrosis was demonstrated at the first office visit, three cases had fat droplets in the blood. Two patients with hemarthrosis of the knee undergoing arthroscopy showed no obvious lesions of intra-articular structures. Instead they showed congestion of the joint capsule located in accordance with the traumatic episode. Magnetic resonance imaging demonstrated marrow abnormalities as diffusely low and high signal intensity areas in T1-weighted and T2-weighted images, respectively, in locations consistent with the traumatic episode and the symptoms. These disappeared within an average of 13 weeks (range in 4 cases, 12 to 16 weeks). These findings were considered diagnostic of bone contusion. Symptom duration was about 2 weeks in all cases. In conclusion the clinician should consider the possibility of coexisting bone contusion in cases of acute traumatic hemarthrosis of the knee with no evidence of bone or intra-articular lesions on clinical examination and conventional radiographs.

Adolescent↗
PubMed1997

Stress fracture of the medial malleolus.

It is difficult to assess the healing of the medial malleolar stress fracture. We describe a case of medial malleolar stress fracture which was monitored its healing with repeated magnetic resonance images.

Adolescent↗
PubMed1995

Atomic model of a pyrimidine dimer excision repair enzyme complexed with a DNA substrate: structural basis for damaged DNA recognition.

T4 endonuclease V is a DNA repair enzyme from bacteriophage T4 that catalyzes the first reaction step of the pyrimidine dimer-specific base excision repair pathway. The crystal structure of this enzyme complexed with a duplex DNA substrate, containing a thymine dimer, has been determined at 2.75 A resolution. The atomic structure of the complex reveals the unique conformation of the DNA duplex, which exhibits a sharp kink with a 60 degree inclination at the central thymine dimer. The adenine base complementary to the 5' side of the thymine dimer is completely flipped out of the DNA duplex and trapped in a cavity on the protein surface. These structural features allow an understanding of the catalytic mechanism and implicate a general mechanism of how other repair enzymes recognize damaged DNA duplexes.

Adenine↗
PubMed1995

Identification of four acidic amino acids that constitute the catalytic center of the RuvC Holliday junction resolvase.

Escherichia coli RuvC protein is a specific endonuclease that resolves Holliday junctions during homologous recombination. Since the endonucleolytic activity of RuvC requires a divalent cation and since 3 or 4 acidic residues constitute the catalytic centers of several nucleases that require a divalent cation for the catalytic activity, we examined whether any of the acidic residues of RuvC were required for the nucleolytic activity. By site-directed mutagenesis, we constructed a series of ruvC mutant genes with similar amino acid replacements in 1 of the 13 acidic residues. Among them, the mutant genes with an alteration at Asp-7, Glu-66, Asp-138, or Asp-141 could not complement UV sensitivity of a ruvC deletion strain, and the multicopy mutant genes showed a dominant negative phenotype when introduced into a wild-type strain. The products of these mutant genes were purified and their biochemical properties were studied. All of them retained the ability to form a dimer and to bind specifically to a synthetic Holliday junction. However, they showed no, or extremely reduced, endonuclease activity specific for the junction. These 4 acidic residues, which are dispersed in the primary sequence, are located in close proximity at the bottom of the putative DNA binding cleft in the three-dimensional structure. From these results, we propose that these 4 acidic residues constitute the catalytic center for the Holliday junction resolvase and that some of them play a role in coordinating a divalent metal ion in the active center.

Aspartic Acid↗
PubMed1995

Crystal structure of a pyrimidine dimer-specific excision repair enzyme from bacteriophage T4: refinement at 1.45 A and X-ray analysis of the three active site mutants.

Crystallographic study of bacteriophage T4 endonuclease V, which is involved in the initial step of the pyrimidine dimer-specific excision repair pathway, has been carried out with respect to the wild-type and three different mutant enzymes. This enzyme catalyzes the cleavage of the N-glycosyl bond at the 5'-side of the pyrimidine dimer, and subsequently incises the phosphodiester bond at the apyrimidinic site through a beta-elimination reaction. The structure of the wild-type enzyme refined at 1.45 A resolution reveals the detailed molecular architecture. The enzyme is composed of a single compact domain classified as an all-alpha structure. The molecule is stabilized mainly by three hydrophobic cores, two of which include many aromatic side-chain interactions. The structure has a unique folding motif, where the amino-terminal segment penetrates between two major alpha-helices and prevents their direct contact, and it is incompatible with the close-packing category of helices for protein folding. The concave surface, covered with many positive charges, implies an interface for DNA binding. The glycosylase catalytic center, which comprises Glu23 and the surrounding basic residues Arg3, Arg22 and Arg26, lie in this basic surface. The crystal structures of the three active-site mutants, in which Glu23 was replaced by Gln(E23Q) and Asp (E23D), respectively, and Arg3 by Gln (R3Q), have been determined at atomic resolution. The backbone structures of the E23Q and R3Q mutants were almost identical with that of the wild-type, while the E23D mutation induces a small, but significant, change in the backbone structure, such as an increase of the central kink of the H1 helix at Pro25. In the catalytic center of the glycosylase, however, these three mutations do not generate notable movements of protein atoms, except for significant shifts of some bound water molecules. Thus, the structural differences between the wild-type and each mutant are confined to the remarkably small region around their replaced chemical groups. Combined with the biochemical studies and the difference circular dichroism measurements, these results allow us to conclude that the negatively charged carboxyl group of Glu23 is essential for the cleavage of the N-glycosyl bond, and that the positively charged guanidino group of Arg3 is crucial to bind the substrate, a DNA duplex containing a pyrimidine dimer. The amino terminal alpha-amino group is located at a position approximately 4.4 A away from the carboxyl group of Glu23. These structural features are generally consistent with the reaction scheme proposed by Dodson and co-workers.

Amino Acid Sequence↗
PubMed1994

Atomic structure of the RuvC resolvase: a holliday junction-specific endonuclease from E. coli.

The crystal structure of the RuvC protein, a Holliday junction resolvase from E. coli, has been determined at 2.5 A resolution. The enzyme forms a dimer of 19 kDa subunits related by a dyad axis. Together with results from extensive mutational analyses, the refined structure reveals that the catalytic center, comprising four acidic residues, lies at the bottom of a cleft that nicely fits a DNA duplex. The structural features of the dimer, with a 30 A spacing between the two catalytic centers, provide a substantially defined image of the Holliday junction architecture. The folding topology in the vicinity of the catalytic site exhibits a striking similarity to that of RNAase H1 from E. coli.

Amino Acid Sequence↗
PubMed1994

Preliminary crystallographic study of Escherichia coli RuvC protein. An endonuclease specific for Holliday junctions.

Single crystals of the RuvC protein, an Escherichia coli endonuclease specific for Holliday junctions, were grown by the microdialysis method. The crystals belong to the space group P2(1), with unit cell dimensions a = 72.8 A, b = 139.6 A, c = 32.4 A and beta = 93.0 degrees, and contain four molecules in an asymmetric unit. Diffraction data to a Bragg spacing of 2.5 A resolution has been obtained using a synchrotron X-ray source.

Bacterial Proteins↗
PubMed1993

Crystal structures of ribonuclease HI active site mutants from Escherichia coli.

In order to investigate the relationships between the three-dimensional structure and the enzymic activity of E. coli RNase HI, three mutant proteins, which were completely inactivated by the replacements of three functional residues, Asp10 by Asn (D10N), Glu48 by Gln (E48Q), and Asp70 by Asn (D70N), were crystallized. Their three-dimensional structures were determined by x-ray crystallography. Although the entire backbone structures of these mutants were not affected by the replacements, very localized conformational changes were observed around the Mg(2+)-binding site. The substitution of an amide group for a negatively charged carboxyl group in common induces the formation of new hydrogen bond networks, presumably due to the cancellation of repulsive forces between carboxyl side chains with negative charges. These conformational changes can account for the loss of the enzymic activity in the mutants, and suggest a possible role for Mg2+ in the hydrolysis. Since the 3 replaced acidic residues are completely conserved in sequences of reverse transcriptases from retroviruses, including human immunodeficiency virus, the concepts of the catalytic mechanism deduced from this structural analysis can also be applied to RNase H activity in reverse transcriptases.

Binding Sites↗
PubMed1993

[Crystal structure and function of pyrimidine dimer specific excision repair enzyme: T4 endonuclease V].

Bacteriophage T4 endonuclease V is an enzyme which plays an important role in pyrimidine dimer specific excision repair of DNA. This enzyme possesses two distinct catalytic activities, pyrimidine dimer glycosylase and apyrimidinic endonuclease. The three dimensional structure (3D) of the wild type enzyme was determined at 1.45A resolution by X-ray crystallography. In combination with the results of site-directed mutagenesis, the refined structure revealed that Glu23 and the surrounding basic residues constitute the catalytic center of this enzyme. Furthermore, the 3D structure of active site mutants were determined and compared with that of the wild type. The results suggest that a precise configuration of Glu23 residue is required for glycosylation and that Arg3 plays an important role in the substrate binding.

Amino Acid Sequence↗
PubMed1992

X-ray structure of T4 endonuclease V: an excision repair enzyme specific for a pyrimidine dimer.

The x-ray structure of T4 endonuclease V, an enzyme responsible for the first step of a pyrimidine-dimer-specific excision-repair pathway, was determined at a 1.6-angstrom resolution. The enzyme consists of a single compact domain classified into an all-alpha structure. This single domain has two distinct catalytic activities; it functions as a pyrimidine dimer glycosylase and as an apurinic-apyrimidinic endonuclease. The amino-terminal segment penetrates between two major helices and prevents their direct contact. The refined structure suggests the residues involved in the substrate binding and the catalysis of the glycosylation reaction.

Amino Acid Sequence↗
PubMed1992

[Treatment of cardial varicose bleeding by trans-ileocolic vein obliteration combined with endoscopic injection sclerotherapy].

In the past 4 years, 11 patients with cardial varix bleeding were experienced. The cardial varices were of 2 types, nodular and serpentine. The nodular varices were caused by gastro-renal shunt and the site of bleeding often existed on the posterior wall. The serpentine cardial varices were an extension of esophageal varices, and the site of bleeding was often on the lesser curvature. The nodular varices had an abundant blood flow. When EIS was performed to these varices independently, the time of contact with the sclerosing agent was so short that no therapeutic effect was obtained. For the purpose of decreasing the blood flow in these varices, TIO was performed first and then EIS was used in the treatment of four cases of nodular varix bleeding. Hemostasis was obtained in two of the four cases with TIO alone, and after the addition of EIS a good hemostatic and varix-reducing effect was noted in all four cases.

Aged↗
PubMed1991

Atomic structure of a pyrimidine-dimer specific excision-repair enzyme from bacteriophage T4.

T4 endonuclease V is an enzyme responsible for the first step of a pyrimidine-dimer specific excision-repair process. The three-dimensional structure of this enzyme has been determined at 1.6A resolution by X-ray crystallography. The enzyme consists of one single compact domain classified into the all alpha structure. This single domain possesses two distinct catalytic activities, a pyrimidine-dimer glycosylase and an apurinic/apyrimidinic endonuclease. The backbone of the enzyme represents a unique folding scheme incompatible with close packing of alpha-helices. The refined structure suggests possible residues that participate in interactions with DNA.

Amino Acid Sequence↗
PubMed1988

Postsynaptic modulation of cholinergic transmission by endogenous substances.

1. Recent concept of postsynaptic modulation is reviewed on the basis of literature data and the results of our investigation using conventional intracellular and voltage-clamp recording methods, in vitro. 2. Experimental evidence provided that the sensitivity of nicotinic ACh receptors endowed on the postsynaptic membrane of the bullfrog sympathetic ganglia and of the frog skeletal muscle end-plate is either facilitated or inhibited by other neurotransmitters or neurohormones. 3. We propose that one neurotransmitter not only initiates its own postsynaptic potential but also regulates the efficacy of synaptic transmission mediated by a distinct neurotransmitter, as an endogenous "antagonist" or "sensitizer".

Animals↗
PubMed1987

Voltage-clamp studies of the inhibition of gamma-aminobutyric acid response by glucocorticoids in bullfrog primary afferent neurons.

Acute effects of glucocorticoids on the response to gamma-aminobutyric acid (GABA) were examined in primary afferent neurons in bullfrog spinal ganglia, using intracellular and voltage-clamp recording techniques. Prednisolone and hydrocortisone (5 microM to 1 mM) caused a dose-dependent decrease in the amplitude of GABA-induced depolarization, while having no effect on the membrane potential and resistance of the neuron. Prednisolone depressed the muscimol-induced depolarization. Nipecotic acid, a blocker of GABA uptake, did not influence the inhibitory action of prednisolone. Voltage-clamp analyses showed that the inward current induced by an iontophoretic application of GABA (GABA current) was suppressed by prednisolone and hydrocortisone. The depression of the GABA current is neither due to a blockage of open channels nor a facilitation of the desensitization of GABA receptors. Prednisolone shifted the dose-response curve of the GABA current downward. The double-reciprocal (Lineweaver-Burk) plot showed that the maximum GABA current was reduced by prednisolone, suggesting a non-competitive antagonism. These results suggest that glucocorticoids suppress the GABA-induced chloride current, decreasing the number of functional channels associated with GABAA receptor.

Afferent Pathways↗