Kiyonori Miyoshi

Bio: Kiyonori Miyoshi is an academic researcher from Kyoto University. The author has contributed to research in topics: Electron paramagnetic resonance & Trigonal bipyramidal molecular geometry. The author has an hindex of 5, co-authored 8 publications receiving 283 citations.

Studies of Metallobleomycins by Electronic Spectroscopy,Electron Spin Resonance Spectroscopy, and Potentiometric Titration

Abstract: The 1:1 bleomycin-A2-Cu(II) complex shows an absorption maximum at 595 nm (epsilon 120), circular dichroism extrema at 555 nm (delta epsilon + 1.21) and 665 nm (-0.61), and electron spin resonance (ESR) signal with g = 2.211, g = 2.055, and A = 178 x 10(-4) cm-1. The formation constant (log K = 12.630) and deprotonation constant (PKc = 3.585) of the 1:1 bleomycin-Cu(II) complex were determined by computer analysis of potentiometric data. The results of potentiometric titration also indicate that the stability of bleomycin-metal complexes is in the order Fe(II) less than Co(II) less than Ni(II) less than Cu(II) greater than Zn(II) and that these divalent metal complexes have a similar coordination environment. The bleomycin-Cu(II) complex has substantially a square-pyramidal configuration in which the secondary amine nitrogen, pyrimidine(N-1) ring nitrogen, deprotonated peptide nitrogen of histidine residue, and histidine imidazole(N-1) nitrogen coordinate to Cu(II) as planar ligand donors, and the alpha-amino nitrogen as axial donor. The specific Cu(II)-binding site of bleomycin has been compared with that of human serum albumin.

Electrochemical and ESR studies on Cu(II) complexes of bleomycin and its related compounds.

Abstract: The 1:1 Cu(II) complexes of bleomycin (BLM) A2, BLM B2, epi-BLM B2, iso-BLM B2, depyruvamide-BLM A2, deglyco-BLM B2 and the structurally related peptides (P-5m, P-3A and P-3) have been comprehensively investigated by ESR and electrochemical methods. ESR spectra for Cu(II) complexes of BLM A2, epi-BLM B2, depyruvamide-BLM A2 and P-3 revealed the axially symmetric g-anisotropies. In contrast, ESR features of the iso-BLM B2, deglyco-BLM B2, P-5m and P-3A complexes, which lack the sixth ligation by the 3-O-carbamoyl group of mannose, exhibited rhombic g-anisotropies with decrease of the A// values. The cyclic voltamograms showed that all of the Cu(II) complexes underwent the well defined quasi-reversible one-electron Cu(II)/Cu(I) coupled redox reaction. The inverse of the redox potential, which measures the effective strength of the ligand field splitting, gave a linear relation with the observed g// value of each Cu(II) complex except for depyruvamide-BLM and P-3. The present results confirmed that the 3-O-carbamoyl group of the mannose moiety of the BLM molecule contributes to the stability of the metal site in BLM-Cu(II) complexes by ligation at the sixth coordination site.

Electron Spin Resonance Study of Cu(II)–Crown Ether Complexes with 3dZ2 Ground State Doublet in Solution

Abstract: Copper(II) chloride and crown ethers (12-crown-4, 15-crown-5 and 18-crown-6) formed orange or orangeyellow complexes in dry chloroform. We found that the ESR g-anisotropy of the complexes was greatly dependent on the numbers of donor oxygens and the ring-numbers. The complexes obtained from 12-crown-4 and 18-crown-6 showed g-anisotropy (g⁄⁄>g⊥); these are well characterized by the 3dx2−y2, or 3dxy ground state. On the other hand, the complexes of 15-crown-5 and its benzo derivatives exhibited the reverse g-anisotropy (g⁄⁄

Bleomycins: towards better therapeutics

Abstract: Bleomycins are a family of glycopeptide antibiotics that have potent antitumour activity against a range of lymphomas, head and neck cancers and germ-cell tumours. The therapeutic efficacy of the bleomycins is limited by development of lung fibrosis. The cytotoxic and mutagenic effects of the bleomycins are thought to be related to their ability to mediate both single-stranded and double-stranded DNA damage, which requires the presence of specific cofactors (a transition metal, oxygen and a one-electron reductant). Progress in understanding the mechanisms involved in the therapeutic efficacy of the bleomycins and the unwanted toxicity and elucidation of the biosynthetic pathway of the bleomycins sets the stage for developing a more potent, less toxic therapeutic agent.

Antioxidant activity of sulfur and selenium: a review of reactive oxygen species scavenging, glutathione peroxidase, and metal-binding antioxidant mechanisms.

Abstract: It is well known that oxidation caused by reactive oxygen species (ROS) is a major cause of cellular damage and death and has been implicated in cancer, neurodegenerative, and cardiovascular diseases. Small-molecule antioxidants containing sulfur and selenium can ameliorate oxidative damage, and cells employ multiple antioxidant mechanisms to prevent this cellular damage. However, current research has focused mainly on clinical, epidemiological, and in vivo studies with little emphasis on the antioxidant mechanisms responsible for observed sulfur and selenium antioxidant activities. In addition, the antioxidant properties of sulfur compounds are commonly compared to selenium antioxidant properties; however, sulfur and selenium antioxidant activities can be quite distinct, with each utilizing different antioxidant mechanisms to prevent oxidative cellular damage. In the present review, we discuss the antioxidant activities of sulfur and selenium compounds, focusing on several antioxidant mechanisms, including ROS scavenging, glutathione peroxidase, and metal-binding antioxidant mechanisms. Findings of several recent clinical, epidemiological, and in vivo studies highlight the need for future studies that specifically focus on the chemical mechanisms of sulfur and selenium antioxidant behavior.

Cellular Copper Transport and Metabolism

Abstract: The transport and cellular metabolism of Cu depends on a series of membrane proteins and smaller soluble peptides that comprise a functionally integrated system for maintaining cellular Cu homeostasis. Inward transport across the plasma membrane appears to be a function of integral membrane proteins that form the channels that select Cu ions for passage. Two membrane-bound Cu-transporting ATPase enzymes, ATP7A and ATP7B, the products of the Menkes and Wilson disease genes, respectively, catalyze an ATP-dependent transfer of Cu to intracellular compartments or expel Cu from the cell. ATP7A and ATP7B work in concert with a series of smaller peptides, the copper chaperones, that exchange Cu at the ATPase sites or incorporate the Cu directly into the structure of Cu-dependent enzymes such as cytochrome c oxidase and Cu, Zn superoxide dismutase. These mechanisms come into play in response to a high influx of Cu or during the course of normal Cu metabolism.