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Y Shiro

Publications and source records attributed to Y Shiro.

82 records · Page 5Linked to original sources
PubMed1990

[A case of mitochondrial myopathy with mononeuritis multiplex].

A case of mitochondrial myopathy with mononeuritis multiplex was described. A 55-year-old man was hospitalized because of blepharoptosis and muscle weakness. His mother also showed blepharoptosis in her elderly stage of life. He had been healthy until 46 years of age, when he first noticed difficulty of speech, followed by bilateral blepharoptosis, weakness of upper limbs, and sensory disturbance in the left occipital, and left upper and lower extremities. These symptoms progressed slowly. On admission, bilateral blepharoptosis was recognized. Slightly to moderate muscle wasting and weakness were observed in the face, neck, trunk, and extremities. Areflexia was observed in the upper extremities. Paresthesia was observed in the left occipital and left hip, and superficial sensation was impaired in the left upper and lower extremities. Electromyographic examination of extremities showed neurogenic changes in the distal muscles and myogenic changes in the proximal muscles. Motor conduction velocities were normal, but sensory conduction velocities decreased in amplitude on the left upper extremity and were not evoked on the left lower extremity. Muscle biopsy specimen revealed numerous "ragged-red" fibers. Cytochrome c oxidase stain showed a decrease in intensity of staining. A sural nerve biopsy showed slight axonal degeneration and slight loss of nerve fibers. Biochemical analysis on biopsy muscle showed partial deficiency of cytochrome c oxidase activity.

Humans↗
PubMed1989

Effect of the distal histidine modification (Cyanation) of myoglobin on the ligand binding kinetics and the heme environmental structures.

The kinetics of carbon monoxide (CO) binding to myoglobin (Mb) modified at the distal histidine (His) by cyanogen bromide (BrCN) has been studied. The CO association and dissociation rates of BrCN-modified Mb were obtained as 1.8 x 10(3) M-1 s-1 and 0.13 s-1, respectively (20 degrees C and pH 7.0). Thermodynamic parameters were obtained as well. These values are notable, compared with those for other hemoproteins, the slowest association and the fastest dissociation rates among various hemoproteins examined so far. On the basis of the available structural data obtained from the absorption, 1H NMR, and IR spectral measurements, these unique kinetic and thermodynamic properties were reasonably explained in terms of the steric restriction at the modified distal side.

Animals↗
PubMed1989

Single-crystal EPR study of novel azide complex of cyanogen bromide-modified myoglobin. Influence of specific modification of the heme distal histidyl residue on the ligand-binding structure.

Stable azide complex of cyanogen bromide-modified met-myoglobin (metMb) was prepared and crystallized. The principal values and eigen vectors of g-tensor were determined by single-crystal EPR spectroscopy at 77 K: gxx = 1.50, gyy = 2.32, and gzz = 2.91. These g values were similar to those of tetrazole derivative rather than azide derivative of native metMbs, suggesting that tetrazole derivative might be formed from N-cyanoimidazole of distal histidyl residue via nucleophilic attack of azide ion by 1,3-dipolar cycloaddition reaction. The orientation of the maximal g value (gzz) of the novel product was found to deviate about 13 degrees from the heme normal of native aquometMb. Thus, the orientation of the heme plane might be altered in passing from native metMb to cyanogen bromide-mediated metmyoglobin. The present EPR results demonstrated that the modification of the histidyl residue at the heme distal side causes the changes in the stereochemical and electronic natures of the ligand binding to the heme.

Azides↗
PubMed1986

Structural characterization of lactoperoxidase in the heme environment by proton NMR spectroscopy.

The heme environmental structures of lactoperoxidase (LP) have been studied by the use of hyperfine-shifted proton NMR and optical absorption spectra. The NMR spectra of the enzyme in native and cyanide forms in H2O indicated that the fifth ligand of the heme iron is the histidyl imidazole with an anionic character and that the sixth coordination site is possibly vacant. These structural characteristics are quite similar to those of horseradish peroxidase (HRP), suggesting that these may be prerequisite to peroxidase activity. The pH dependences of the spectra of LP in cyanide and azide forms showed the presence of two ionizable groups with pK values of 6 and 7.4 in the heme vicinity, which is consistent with the kinetic results. The group with pK = 7.4 is associated with azide binding to LP in a slow NMR exchange limit, which is in contrast to the fast entry of azide to HRP.

Heme↗
PubMed1986

Presence of endogenous calcium ion and its functional and structural regulation in horseradish peroxidase.

The endogenous calcium ion (Ca2+) in horseradish peroxidase (HRP) was removed to cause substantial changes in the proton NMR spectra of the enzyme in various oxidation/spin states. The spectral changes were interpreted as arising from the substantial alterations in the heme environments, most likely the heme proximal and distal sides. The comparative kinetic and redox studies revealed that these conformational changes affect the reduction process of compound II, resulting in the decrease of the enzymatic activity of HRP. It is also revealed from the ESR spectrum and the temperature dependences of the NMR and optical absorption spectra of the Ca2+-free enzyme that the heme iron atom of the Ca2+-free enzyme is in a thermal spin mixing between ferric high and low spin states, in contrast to that of the native enzyme. These results show that Ca2+ functions in maintaining the protein structure in the heme environments as well as the spin state of the heme iron, in favor of the enzymatic activity of HRP.

Calcium↗
PubMed1986

Presence of endogenous calcium ion in horseradish peroxidase. Elucidation of metal-binding site by substitutions of divalent and lanthanide ions for calcium and use of metal-induced NMR (1H and 113Cd) resonances.

Some divalent (Cd2+, Sr2+, Ba2+) and lanthanide (Ln3+) ions can be substituted for endogenous Ca2+ of horseradish peroxidase (HRP, Ca2+-bound hemoenzyme) and maintain the protein structure in the heme vicinity as well as the enzymatic activity of HRP, as does Ca2+. However, due to lower affinity than Ca2+, the bound Ln3+ was readily replaced by Ca2+ to yield native HRP, in sharp contrast to other typical Ca2+-binding proteins, of which the affinity to Ln3+ is higher than to Ca2+. Addition of paramagnetic Ln3+ to Ca2+-free HRP induced a series of paramagnetically shifted 1H NMR resonances of protein at the first metal binding site in HRP. The pH-dependent spectral changes of the Ln3+-shifted resonances suggest that tyrosyl hydroxyl and glutamate and aspartate carboxyl groups are involved in the binding site of the Ca2+, other divalent ions, or Ln3+. The 113Cd NMR spectra of 113Cd2+-bound HRP also indicated the presence of one metal strongly bound to the oxygen ligands and another site with low affinity for the metal ions, which is consistent with the results from the Ln3+-induced proton NMR. All these results suggest that the binding of one metal ion to HRP is essential for its structural and functional properties.

Amino Acids↗
PubMed1986

On the mechanism of the chemical and enzymic oxygenations of alpha-oxyprotohemin IX to Fe.biliverdin IX alpha.

alpha-Oxyprotohemin IX, an early intermediate in heme catabolism, was synthesized and its autoxidation to biliverdin IX alpha was studied. In anaerobic aqueous pyridine, alpha-oxyprotohemin (hexacoordinated) underwent autoreduction to yield an Fe(II) alpha-oxyprotoporphyrin pi-neutral radical bis(pyridine) complex, which reacted with an equimolar amount of dioxygen to give pyridine.verdohemochrome IX alpha and CO in 75-80% yield via an intermediate with an absorption maximum at 893 nm. Verdohemochrome IX alpha did not react with further dioxygen. Reconstituted apomyoglobin.alpha-oxyprotohemin IX complex (pentacoordinated) reacted with an equimolar amount of dioxygen to form an Fe(II) oxyporphyrin pi-neutral radical intermediate, which rearranged to a green compound (lambda max 660 and 704 nm) with elision of CO. The green product, which is probably an apomyoglobin.verdoheme pi-radical complex, reacted with another equimolar amount of dioxygen to give Fe(III).biliverdin IX alpha. Demetallation of this gave biliverdin IX alpha in overall yield of 70-75%. These results indicate that the sequence of oxyheme autoxidation in the presence of apomyoglobin is alpha-oxyprotoheme IX O2----CO----verdohemochrome IX alpha pi-radical O2----Fe(III).biliverdin IX alpha. A similar mechanism may prevail in vivo. The hexa- and pentacoordinated Fe(II) pi-radical form of the oxyporphyrin is crucial in triggering the autoxidation of the complex to verdohemochrome IX alpha. Further oxygenation of verdohemochrome IX alpha to Fe(III).biliverdin IX alpha occurred only in the pentacoordinated apomyoglobin.verdoheme Fe(II) complex.

Apoproteins↗
PubMed1984

Modification of the heme distal side in myoglobin by cyanogen bromide. Heme environmental structures and ligand binding properties of the modified myoglobin.

Met, deoxy, and CO forms of myoglobin (Mb) react with a stoichiometric amount of cyanogen bromide (BrCN) to cause substantial changes in the 1H NMR, optical absorption, and infrared spectra. These spectral changes were interpreted as arising from the substantial alterations in the heme environments, most probably due to the modification of the histidine residue at the heme distal side. It is also revealed that the modified Mb does not combine with some exogenous ligands such as CN-, CH3NH2, and O2, although it does with N-3 or CO. These unique ligand binding properties are also discussed with relevance to a role of the distal histidine in stabilizing the coordinated ligand through a hydrogen bond and to a steric constraint.

Animals↗