Sources of Cd include welding emissions, electronic components and NiCd batteries. EU and US legislations are now in place to reduce our exposure to Cd. Once absorbed into the body, Cd is targeted by metallothioneins, cysteine, the tripeptide glutathione and the protein albumin (Fig. 29.32) and is transported in the blood to the liver. 

(a) What features are highlighted in ball-and-stick representation in Fig. 29.32? Suggest how they originate in terms of the amino acid residues present in the protein. 

(b) Why are metallothioneins, cysteine, glutathione and albumin suited to binding Cd²⁺? 

(c) Give examples of other metal ions transported by metallothioneins.

Figure 29.32.