当前位置： SCI文献检索 > BIOCHEMISTRY期刊下所有文献 > Cu(II) coordination in arthropod and mollusk green half-methemocyanins analyzed by electron spin-echo envelope modulation spectroscopy.

Cu(II) coordination in arthropod and mollusk green half-methemocyanins analyzed by electron spin-echo envelope modulation spectroscopy.

Abstract：

:Hemocyanin (Hc) is a dinuclear copper protein that binds oxygen reversibly. The structure of the Cu(II) site in a derivative of hemocyanin known as green half-met (GHM) has been analyzed using the pulsed EPR technique of electron spin-echo envelope modulation (ESEEM) spectroscopy. The derivative, prepared by treating the native protein with nitrite at low pH, contains a mixed-valent binuclear copper center. It was shown through chemical assays and the ligand exchange reaction products identified by EPR spectroscopy to contain a nitrite ligand bound to Cu(II). The ESEEM spectra of green half-methemocyanins from mollusks and arthropods indicated that three imidazole ligands are coordinated to Cu(II). Therefore, a tetragonal N3O ligand structure (O is an oxygen of nitrite) is proposed. For GHM Hc from the mollusks Octopus vulgaris and Rapana thomasiana, the isotropic nitrogen nuclear hyperfine coupling constant, aiso, for the N delta (or remote) nitrogen of two imidazoles was approximately 1.4 MHz, while for the third, aiso congruent to 2.2 MHz. The difference between the two weaker nitrogens and the single, more strongly coupled nitrogen was smaller by 0.2 MHz in the GHM Hcs from the arthropods Carcinus maenas, Homarus americanus and Panulirus interruptus. The nitrogen nuclear quadrupole coupling constants and asymmetry parameters, e2Qq and eta, for the N delta nitrogens in nearly all cases were near 1.4 MHz and 0.8, respectively, although Rapana thomasiana GHM Hc exhibited a reduction in eta that may indicate weaker hydrogen bonding in the active site of this protein. The g and ACu (copper nuclear hyperfine coupling) values for the derivatives, and the finding of three similar nuclear hyperfine coupling constants for the N delta sites of imidazole ligands, when considered with the orientation-specific information obtained using angle-selection methods for simulation of ESEEM spectra, suggest a distorted tetragonal Cu(II) structure in which three imidazoles and a nitrite ligand are bound near the equatorial plane. The finding that the two molluscan GHM Hcs exhibit differences associated with the remote nitrogen of imidazoles bound to Cu(II) may be related to a structural variability in the active sites of these proteins not found in the arthropodan GHM Hcs examined.

journal_name

Biochemistry

journal_title

Biochemistry

authors

Magliozzo RS,Bubacco L,McCracken J,Jiang F,Beltramini M,Salvato B,Peisach J

doi

10.1021/bi00005a007

subject

Has Abstract

pub_date

1995-02-07 00:00:00

pages

1513-23

issue

eissn

0006-2960

issn

1520-4995

journal_volume

pub_type

杂志文章

在线工具

Cu(II) coordination in arthropod and mollusk green half-methemocyanins analyzed by electron spin-echo envelope modulation spectroscopy.