Metal release in metallothioneins induced by nitric oxide: X-ray absorption spectroscopy study.

Metallothioneins (MTs) are low molecular weight proteins that include metal ions in thiolate clusters. The capability of metallothioneins to bind different metals has suggested their use as biosensors for different elements. We study here the interaction of nitric oxide with rat liver MTs by using in situ X-ray absorption spectroscopy techniques. We univocally show that the presence of NO induces the release of Zn atoms from the MT structure to the solution. Zn ions transform in the presence of NO from a tetrahedral four-fold coordinated environment in the MT into a regular octahedral six-fold coordinated state, with interatomic distances compatible with those of Zn solvated in water.