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Kinetics of the reconstitution of hemoglobin from semihemoglobins α and β with heme (1992)

Kawamura-Konishi, Yasuko ; Chiba, Kaori ; Kihara, Hiroshi ; [et al.]

Springer

European biophysics journal 21 (1992), S. 85-92

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ISSN: 1432-1017

Keywords: Hemoglobin ; Semihemoglobin ; Reconstitution ; Stopped-flow

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Physics

Notes: Abstract Kinetics of the reconstitution of hemoglobin from semihemoglobins α and β with hemin dicyanide have been investigated using three kinds of stopped-flow technique (Soret absorption, fluorescence quenching of tryptophan, and Soret CD). The semihemoglobins α and β are occupied by heme in the α and β chains, respectively, the other chain being heme-free. Based on the kinetic results, the following scheme for the reconstitution is proposed; First, hemin dicyanide enters the pocket-like site of the apo chains. Second, in semihemoglobin α, the CN-ligand in the fifth coordination position of iron is replaced by the imidazole ring of the proximal His immediately after the heme insertion. In contrast, semihemoglobin β changes its conformation after the heme insertion, and this is followed by the ligand replacement. Finally, the partial structure changes induced by the ligand replacement propagate onto the whole molecule and the final conformation is attained. The results indicate that semihemoglobin α retains a more rigid and organized structure, and more closely approaches its final structure than does semihemoglobin β.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00185423

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Kinetic study on myoglobin refolding monitored by five optical probe stopped-flow methods (1994)

Chiba, Kaori ; Ikai, Atsushi ; Kawamura-Konishi, Yasuko ; [et al.]

New York, NY : Wiley-Blackwell

Proteins: Structure, Function, and Genetics 19 (1994), S. 110-119

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ISSN: 0887-3585

Keywords: folding intermediate ; urea denaturation ; stopped-flow circular dichroism ; molten globule ; hemindicyanide ; Chemistry ; Biochemistry and Biotechnology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine

Notes: The refolding kinetics of horse cyanometmyoglobin induced by concentration jump of urea was investigated by five optical probe stopped-flow methods: absorption at 422 nm, tryptophyl fluorescence at around 340 nm, circular dichroism (CD) at 222 nm, CD at 260 nm, and CD at 422 nm. In the refolding process, we detected three phases with rate constants of 〉 1 × 102 s-1, (4.5-9.3) S-1, and (2-5) × 10-3 s-1. In the fastest phase, a substantial amount of secondary structure (40%) is formed within the dead time of the CD stopped-flow apparatus (10.7 ms). The kinetic intermediate populated in the fastest phase is shown to capture a hemindicyanide, suggesting that a “heme pocket precursor” recognized by hemindicyanide must be constructed within the dead time. In the middle phase, most of secondary and tertiary structures, especially around the captured hemindicyanide, have been constructed. In the slowest phase, we detected a minor structural rearrangement accompanying the ligand-exchange reaction in the fifth coordination of ferric iron. We present a possible model for the refolding process of myoglobin in the presence of the heme group. © 1994 Wiley-Liss, Inc.

Additional Material: 8 Ill.