Biliverdin-copper complex at physiological pH
Milena S. Dimitrijević (University of Belgrade)
Jelena Bogdanović Pristov (University of Belgrade)
Milan Žižić (University of Belgrade)
Dalibor M. Stanković (University of Belgrade)
Danica Bajuk-Bogdanović (University of Belgrade)
Marina Stanić (University of Belgrade)
Snežana Spasić (University of Belgrade)
Wilfred Hagen (TU Delft - BT/Biocatalysis)
Ivan Spasojević (University of Belgrade)
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Abstract
Biliverdin (BV), a product of heme catabolism, is known to interact with transition metals, but the details of such interactions under physiological conditions are scarce. Herein, we examined coordinate/redox interactions of BV with Cu
2+
in phosphate buffer at pH 7.4, using spectrophotometry, HESI-MS, Raman spectroscopy,
1
H NMR, EPR, fluorimetry, and electrochemical methods. BV formed a stable coordination complex with copper in 1:1 stoichiometry. The structure of BV was more planar and energetically stable in the complex. The complex showed strong paramagnetic effects that were attributed to an unpaired delocalized e
-
. The delocalized electron may come from BV or Cu
2+
, so the complex is formally composed either of BV radical cation and Cu
1+
or of BV radical anion and Cu
3+
. The complex underwent oxidation only in the presence of both O
2
and an excess of Cu
2+
, or a strong oxidizing agent, and it was resistant to reducing agents. The biological effects of the stable BV metallocomplex containing a delocalized unpaired electron should be further examined, and may provide an answer to the long-standing question of high energy investment in the catabolism of BV, which represents a relatively harmless molecule per se.