Table 3 Cu isotope compositions of sulfur (S) and nitrogen (N) bonding environments across levels of biological complexity.

From: Metal-binding amino acid ligands commonly found in metalloproteins differentially fractionate copper isotopes

Biocomplexity level

Source

S-rich bonding environment

N-rich bonding environment

Δ65CuS-N (‰)a

Reference

Amino acids

Experimental

Cysteine

Histidine

− 0.47 ± 0.18b

This study

Amino acids

Theoretical

Cysteine

Histidine

− 1.13

Fujii et al.4

Proteins

Human cortices (healthy and Alzheimer’s)

Metallothionein

Cu,Zn superoxide dismutase

− 0.61 ± 0.34b

Larner et al.17

Proteins

Saccharomyces

Metallothionein

Cu,Zn superoxide dismutase

− 0.53

Zhu et al.34

Tissues

Humans (healthy)

Blood serum

Red blood cells

− 0.82 ± 0.64b

Albarède et al.8

  1. aFor amino acids (experimental and theoretical), this value is the difference between Δ65Cucysteine-free and Δ65Cuhistidine-free, where ‘free’ refers to ions in water.
  2. bError propagated from two times the standard error of individual samples (experiments or subjects).
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