Junji Teraoka

LOOP STRUCTURE IN HUMAN SERUM ALBUMIN FROM RAMAN OPTICAL ACTIVITY

Vibrational Raman optical activity (ROA) measurements on human serum albumin are reported and discussed. At neutral pH, the ROA spectrum in the normal state N is dominated by bands assigned to α-helix together with a strong positive ROA band at ca. 1340 cm-1 assigned to a loop structure with local order possibly that of a 310-helix. On reducing the pH to 3.4, which generates the molten globule-like F state, only small decreases in the α-helix ROA bands occur, but the ca. 1340 cm-1 band decreases by ca. 40%, reflecting a loss of rigidity of part of the loop structure, possibly involving residues 292–315 since these connect the two halves of the molecule thought to be dissociated in the F state. These results suggest that the long loops comprising residues 106–119, 292–315 and 492–511 which connect subdomains A and B within each of the three domains I, II and III and previously described from x-ray studies simply as extended polypeptide might in fact have local order of a 310-helix.

Resonance Raman study of plant tissue peroxidases Common characteristics in iron coordination environments

Abstract Resonance Raman spectra of isozymes 2, 3, 9, 15, and 16 of Japanese radish peroxidase and isozymes 1, 3, and 7 of turnip peroxidase were measured and compared with those of horseradish peroxidase. All the resting isozymes gave the ν 10 band around 1629–1631 cm −1 , indicating the five-coordinate high-spin structure. The reduced form of all these isozymes provided the iron-histidine stretching Raman line at distinctly higher frequencies in comparison with those of hemoglobin and exhibited a clear pH-dependent frequency shift at neutral pH in accord with the results for horseradish peroxidase. Therefore, we conclude that strong hydrogen bonding of the proximal histidine and a small structural change of the proximal histidine at neutral pH without breakage of the hydrogen bond are the common characteristics of plant tissue peroxidases (EC 1.11.1.7) which contrast with those of oxygen-carrier hemoproteins.

Mixed-ligand rare earth complexes of phthalocyanine and β-diketones☆

Abstract Refluxing tris(β-diketonato) complexes of rare earth elements (Ln) with dilithium phthalocyaninate (Li2Pc) in dried organic solvents resulted in mixed-ligand complexes of diverse composition depending on the β-diketones and solvents used. With dipivaloylmethane (dpmH) used as the β-diketone, two types of novel complexes, Ln2Pc(dpm)4 and [LnPc · (dpm)2]2, were obtained. By X-ray analysis the samarium complex of the former type was shown to have an axially symmetric Pc bridge binding two Sm atoms. The complexes of the latter type have an unpaired electron on the Pc ligand, as proved by the paramagnetism of the yttrium compound, and seem to be formed by atmospheric oxidation during the reflux. Other types of complexes obtained are: LnPc(dbm)(solv)2, LnPcH(dbm)2(solv)2 and LnPcH(acac)2 where dbmH = dibenzoylmethane and acacH = acetylacetone. The magnetic susceptibilities of the binuclear series Ln2Pc(dpm)4 conformed to the van Vleck-Frank formula down to 77 K, except that complexes with Ln ≡ Er, Tm and Yb gave somewhat large absolute values of the Curie-Weiss constants (θ = 23, 20 and −50 K where χ = C (T − θ) ). A comparative study disclosed that Yb(dpm)3 and even YbCl3 · 6H2O gave θ also in the neighborhood of −50 K, although Tm(dpm)3 and Er(dpm)3 showed θ values close to 0.

Resonance Raman characterization of porphycene anions

Resonance Raman spectra of reduced porphycenes were measured in an effort to characterize structural changes concomitant with chemical reduction. Frequency shifts were observed for reduced porphycenes in certain skeletal vibrational modes. The observed resonance Raman behavior was generally consistent with the results of vibrational analysis by quantum chemical calculations based on density functional methods.

Resonance Raman spectra of highly reduced iron porphycenes

The redox behavior of iron porphycenes using the sodium mirror contact technique is reported. The resonance Raman spectra are obtained for each redox state, in order to explore the vibrational characteristics of these species in different redox states. The observed resonance Raman behavior of FeII porphycene anion radical and its dianion is interpreted using the vibrational analysis of free-base porphycene anion radical and dianion. For the first time, a species generated in the fourth reduction step, is confirmed by UV-vis spectroscopy and is assigned to FeI porphycene π dianion. The dependence of resonance enhancements of Raman bands for the FeI porphycene π dianion on excitation laser reveals structural distortion along the NCaCaN or CbCaCaCb segments of the pyrrole-pyrrole direct connection in the excited electronic state.

Resonance Raman spectra of N-deprotonated σ-type dianion of porphycenes

Resonance Raman spectra of N-deprotonated sigma-type dianion of porphycenes were measured in an effort to characterize the structural changes concomitant with N-deprotonation. The observed resonance Raman behavior was consistent with the results of vibrational analysis by quantum chemical calculations based on density functional theory methods. Resonance Raman behavior predicted an expanded porphycene core for N-deprotonated sigma-type dianion with elongation of peripheral bond lengths. This sigma-type dianion is distinctive from pi-type dianion which has an expanded core with alternating changes in peripheral bond lengths.

Vibrational Circular Dichroism of Ligand Vibrations in Hemeprotein

The distal amino acid residues in myoglobin (Mb) and hemoglobin (Hb) are elaborately designed to control the chemical reactions of ligands to the heme iron. Many techniques have been applied to elucidate the reaction mechanism of ligand binding in heme pockets. Recently, vibrational circular dichroism (VCD) has emerged as a promising technique for investigating the coordination geometry of ligands bound to heme proteins.1 In the present study the time evolution of VCD band of azide ligand of reconstituted myoglobin was measured to obtain new insights into the stereochemical structure of coordination geometry of heme ligands and the VCD of a model system of a C2 chiral strapped iron porphyrin was studied for understanding the VCD origin of heme ligand vibration.