Equilibrium binding constants and facile dissociation of novel serum albumin-dicyanoaurate(I) complexes

Annapurna J. Canumalla; S. Schraa; Anvarhusein A. Isab; C. Frank Shaw; E. Gleichmann; L. Dunemann; M. Turfeld

doi:10.1007/s007750050203

Equilibrium binding constants and facile dissociation of novel serum albumin-dicyanoaurate(I) complexes

Annapurna J. Canumalla, S. Schraa, Anvarhusein A. Isab, C. Frank Shaw^*, E. Gleichmann, L. Dunemann, M. Turfeld

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

20 Scopus citations

Abstract

Dicyanoaurate(I), Au(CN)₂/^-, an important metabolite of chrysotherapy agents (anti-arthritic gold drugs), contains two tightly bound cyanide ligands which render it relatively unreactive toward ligand exchange reactions with potential gold-binding ligands. The extent and nature of its binding to bovine serum albumin (BSA), which may modulare the in vivo activity of Au(CN₂/^-, were investigated to determine whether Au(CN)₂/^- might be more bioavailable than other gold complexes. ¹³C NMR spectroscopy, radioisotope tracers, chromatography, ultrafiltration, and atomic spectroscopy, employing Au(¹³CN)₂/^- or Au(¹⁴N)₂/^- as appropriate, revealed two distinct binding mechanisms. The dominant reaction is reversible association (nonspecific binding) of intact Au(CN)₂/^- ions to form BSA·[Au(CN)₂/^-](n) adducts. Approximately one equivalent binds with an equilibrium binding constant (pH 7.4, 25°C) of K¹=5.5 (±1.1) x 10⁴, and three additional equivalents bind with a constant of 7.0 (±0.1)x10³. Au(¹³CN)₂/^- associated with albumin is characterized by a broad ¹³ NMR resonance at δ(c)=154.7 ppm compared to the sharp resonance of the free complex at 156.4 ppm. The BSA·[Au(CN)₂/^-](n) adducts readily dissociate during gel exclusion chromatography and are therefore underestimated, but are retained and accurately quantitated by ultrafiltration methods. The second binding mechanism is a ligand exchange reaction at Cys-34, to form AlbSAuCN, which accounts for only a small fraction (≤11%) of the bound gold. The small extent of the latter interaction differentiates Au(CN)₂/^- from the gold drugs such as auranofin, aurothiomalate (Myochrysin) and aurothioglucose (Solganol), which undergo ligand exchange at Cys-34 of albumin to form tightly bound gold-protein complexes. The weak interaction at Cys-34 and the facile dissociation of bound, intact Au(CN)₂/^- are consistent with its putative role as a gold metabolite that can be accumulated intracellularly.

Original language	English
Pages (from-to)	9-17
Number of pages	9
Journal	Journal of Biological Inorganic Chemistry
Volume	3
Issue number	1
DOIs	https://doi.org/10.1007/s007750050203
State	Published - Feb 1998

Bibliographical note

Funding Information:
Acknowledgements CFS thanks the Deutsche Forschungsge-meinschaft (DFG) for a Gast Professorship at the Medizinisches Institut für Umwelthygiene during the 1993–94 academic year and the University of Wisconsin Milwaukee for a sabbatical leave. This research was supported by the US NIH (AR 39902) and the DFG.

Keywords

Bovine serum albumin
C NMR
Dicyanoaurate(I)
Equilibrium binding constants
Labile dissociation

ASJC Scopus subject areas

Biochemistry
Inorganic Chemistry

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10.1007/s007750050203

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@article{c156cfd90e4f480c83d63fe3dfa56881,

title = "Equilibrium binding constants and facile dissociation of novel serum albumin-dicyanoaurate(I) complexes",

abstract = "Dicyanoaurate(I), Au(CN)2/-, an important metabolite of chrysotherapy agents (anti-arthritic gold drugs), contains two tightly bound cyanide ligands which render it relatively unreactive toward ligand exchange reactions with potential gold-binding ligands. The extent and nature of its binding to bovine serum albumin (BSA), which may modulare the in vivo activity of Au(CN2/-, were investigated to determine whether Au(CN)2/- might be more bioavailable than other gold complexes. 13C NMR spectroscopy, radioisotope tracers, chromatography, ultrafiltration, and atomic spectroscopy, employing Au(13CN)2/- or Au(14N)2/- as appropriate, revealed two distinct binding mechanisms. The dominant reaction is reversible association (nonspecific binding) of intact Au(CN)2/- ions to form BSA·[Au(CN)2/-](n) adducts. Approximately one equivalent binds with an equilibrium binding constant (pH 7.4, 25°C) of K1=5.5 (±1.1) x 104, and three additional equivalents bind with a constant of 7.0 (±0.1)x103. Au(13CN)2/- associated with albumin is characterized by a broad 13 NMR resonance at δ(c)=154.7 ppm compared to the sharp resonance of the free complex at 156.4 ppm. The BSA·[Au(CN)2/-](n) adducts readily dissociate during gel exclusion chromatography and are therefore underestimated, but are retained and accurately quantitated by ultrafiltration methods. The second binding mechanism is a ligand exchange reaction at Cys-34, to form AlbSAuCN, which accounts for only a small fraction (≤11\%) of the bound gold. The small extent of the latter interaction differentiates Au(CN)2/- from the gold drugs such as auranofin, aurothiomalate (Myochrysin) and aurothioglucose (Solganol), which undergo ligand exchange at Cys-34 of albumin to form tightly bound gold-protein complexes. The weak interaction at Cys-34 and the facile dissociation of bound, intact Au(CN)2/- are consistent with its putative role as a gold metabolite that can be accumulated intracellularly.",

keywords = "Bovine serum albumin, C NMR, Dicyanoaurate(I), Equilibrium binding constants, Labile dissociation",

author = "Canumalla, \{Annapurna J.\} and S. Schraa and Isab, \{Anvarhusein A.\} and Shaw, \{C. Frank\} and E. Gleichmann and L. Dunemann and M. Turfeld",

note = "Funding Information: Acknowledgements CFS thanks the Deutsche Forschungsge-meinschaft (DFG) for a Gast Professorship at the Medizinisches Institut f{\"u}r Umwelthygiene during the 1993–94 academic year and the University of Wisconsin Milwaukee for a sabbatical leave. This research was supported by the US NIH (AR 39902) and the DFG.",

year = "1998",

month = feb,

doi = "10.1007/s007750050203",

language = "English",

volume = "3",

pages = "9--17",

journal = "Journal of Biological Inorganic Chemistry",

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publisher = "Springer Science and Business Media Deutschland GmbH",

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TY - JOUR

T1 - Equilibrium binding constants and facile dissociation of novel serum albumin-dicyanoaurate(I) complexes

AU - Canumalla, Annapurna J.

AU - Schraa, S.

AU - Isab, Anvarhusein A.

AU - Shaw, C. Frank

AU - Gleichmann, E.

AU - Dunemann, L.

AU - Turfeld, M.

N1 - Funding Information: Acknowledgements CFS thanks the Deutsche Forschungsge-meinschaft (DFG) for a Gast Professorship at the Medizinisches Institut für Umwelthygiene during the 1993–94 academic year and the University of Wisconsin Milwaukee for a sabbatical leave. This research was supported by the US NIH (AR 39902) and the DFG.

PY - 1998/2

Y1 - 1998/2

N2 - Dicyanoaurate(I), Au(CN)2/-, an important metabolite of chrysotherapy agents (anti-arthritic gold drugs), contains two tightly bound cyanide ligands which render it relatively unreactive toward ligand exchange reactions with potential gold-binding ligands. The extent and nature of its binding to bovine serum albumin (BSA), which may modulare the in vivo activity of Au(CN2/-, were investigated to determine whether Au(CN)2/- might be more bioavailable than other gold complexes. 13C NMR spectroscopy, radioisotope tracers, chromatography, ultrafiltration, and atomic spectroscopy, employing Au(13CN)2/- or Au(14N)2/- as appropriate, revealed two distinct binding mechanisms. The dominant reaction is reversible association (nonspecific binding) of intact Au(CN)2/- ions to form BSA·[Au(CN)2/-](n) adducts. Approximately one equivalent binds with an equilibrium binding constant (pH 7.4, 25°C) of K1=5.5 (±1.1) x 104, and three additional equivalents bind with a constant of 7.0 (±0.1)x103. Au(13CN)2/- associated with albumin is characterized by a broad 13 NMR resonance at δ(c)=154.7 ppm compared to the sharp resonance of the free complex at 156.4 ppm. The BSA·[Au(CN)2/-](n) adducts readily dissociate during gel exclusion chromatography and are therefore underestimated, but are retained and accurately quantitated by ultrafiltration methods. The second binding mechanism is a ligand exchange reaction at Cys-34, to form AlbSAuCN, which accounts for only a small fraction (≤11%) of the bound gold. The small extent of the latter interaction differentiates Au(CN)2/- from the gold drugs such as auranofin, aurothiomalate (Myochrysin) and aurothioglucose (Solganol), which undergo ligand exchange at Cys-34 of albumin to form tightly bound gold-protein complexes. The weak interaction at Cys-34 and the facile dissociation of bound, intact Au(CN)2/- are consistent with its putative role as a gold metabolite that can be accumulated intracellularly.

AB - Dicyanoaurate(I), Au(CN)2/-, an important metabolite of chrysotherapy agents (anti-arthritic gold drugs), contains two tightly bound cyanide ligands which render it relatively unreactive toward ligand exchange reactions with potential gold-binding ligands. The extent and nature of its binding to bovine serum albumin (BSA), which may modulare the in vivo activity of Au(CN2/-, were investigated to determine whether Au(CN)2/- might be more bioavailable than other gold complexes. 13C NMR spectroscopy, radioisotope tracers, chromatography, ultrafiltration, and atomic spectroscopy, employing Au(13CN)2/- or Au(14N)2/- as appropriate, revealed two distinct binding mechanisms. The dominant reaction is reversible association (nonspecific binding) of intact Au(CN)2/- ions to form BSA·[Au(CN)2/-](n) adducts. Approximately one equivalent binds with an equilibrium binding constant (pH 7.4, 25°C) of K1=5.5 (±1.1) x 104, and three additional equivalents bind with a constant of 7.0 (±0.1)x103. Au(13CN)2/- associated with albumin is characterized by a broad 13 NMR resonance at δ(c)=154.7 ppm compared to the sharp resonance of the free complex at 156.4 ppm. The BSA·[Au(CN)2/-](n) adducts readily dissociate during gel exclusion chromatography and are therefore underestimated, but are retained and accurately quantitated by ultrafiltration methods. The second binding mechanism is a ligand exchange reaction at Cys-34, to form AlbSAuCN, which accounts for only a small fraction (≤11%) of the bound gold. The small extent of the latter interaction differentiates Au(CN)2/- from the gold drugs such as auranofin, aurothiomalate (Myochrysin) and aurothioglucose (Solganol), which undergo ligand exchange at Cys-34 of albumin to form tightly bound gold-protein complexes. The weak interaction at Cys-34 and the facile dissociation of bound, intact Au(CN)2/- are consistent with its putative role as a gold metabolite that can be accumulated intracellularly.

KW - Bovine serum albumin

KW - C NMR

KW - Dicyanoaurate(I)

KW - Equilibrium binding constants

KW - Labile dissociation

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DO - 10.1007/s007750050203

M3 - Article

AN - SCOPUS:0031931428

SN - 0949-8257

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EP - 17

JO - Journal of Biological Inorganic Chemistry

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ER -

Equilibrium binding constants and facile dissociation of novel serum albumin-dicyanoaurate(I) complexes

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

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