Purification of metallothionein by fast protein liquid chromatography

Characterization of metallothionein isoforms from rabbit liver by liquid chromatography coupled to electrospray mass spectrometry

Metallothioneins (MTs), a group of low molecular weight proteins found in practically all life forms, are characterized by high sulfur content and an affinity for metal ions. At acidic pH, MTs show metal depletion, leading to apothioneins. In the work described here, in order to optimize the separation of rabbit liver apothioneins using liquid chromatography (LC) with UV detection, the proportion of the organic modifier of the mobile phase was optimized by establishing relationships between Reichardt's E(N)(T) scale of solvent polarity and the chromatographic retention measured by the capacity factor, k. Additionally, such optimum separations were carried out in a LC-electrospray mass spectrometry (ES-MS) coupled system allowing the identification and characterization of the different rabbit liver apo-MT-forms. In this way, electrospray ionization mass spectrometry offers great possibilities aiming at a better understanding of metallothionein polymorphism.

Polymorphism and identification of metallothionein isoforms by reversed-phase HPLC with on-line ion-spray mass spectrometric detection

Microbore reversed-phase HPLC with on-line ion-spray mass spectrometric detection is proposed for a study of polymorphism of rabbit liver metallothionein (MTRL) and its major isoforms MT-1 and MT-2. Separation conditions had been optimized until each chromatographic peak could be attributed to a single metalloprotein species, of which the molecular mass could be determined by ionspray MS. At the optimized conditions (elution with the gradient 5-8% of acetonitrile within 50 min using a 5 mM acetate buffer at pH 6), the chromatogram of MTRL showed five peaks, whereas those of MT-1 and MT-2 showed nine and seven different peaks, respectively. The on-line determination of the molecular masses (+/- 1 Da) of the compounds eluted permits the unambiguous cataloguing and further referencing of putative and true MT subisoforms. The results obtained are compared with those obtained by direct ion-spray MS of the MT preparations at different pHs, with a goal to identify possible chromatographic artifacts. Metals (Cd, Cu) in the eluted complexes were studied by HPLC with on-line ICP MS detection.