Spectroscopic characterization of native and Co(II)-substituted zucchini mavicyanin

Abstract

 Mavicyanin from zucchini peelings has been characterized by electronic absorption, circular dichroism (CD), magnetic circular dichroism (MCD), resonance Raman (RR), and electron paramagnetic resonance (EPR) spectra. The electronic absorption, CD, MCD, and EPR spectra are appreciably similar to those of stellacyanin from lacquer, in which the tetrahedral Cu center has a donor set composed of four amino acid residues [2 histidine (His), cysteine (Cys), and glutamine (Gln)]. Under neutral conditions, mavicyanin and stellacyanin show intense blue bands at 599 and 604 nm, respectively. However, the RR spectrum of mavicyanin between 300 and 450 cm^–1, which is believed to originate from the predominant Cu–S stretching vibration, is remarkably different from that of stellacyanin. This might be due to a slight distortion of the tetrahedral Cu(II) center toward tetragonal geometry in mavicyanin. Moreover, the d–d transition bands of Co(II)-substituted mavicyanin are slightly blue-shifted compared with those of Co(II)-substituted stellacyanin. This finding also suggests a difference in distortion between these tetrahedral Co(II) centers in spite of the same donor sets.