POLYMORPHISM AND IDENTIFICATION OF METALLOTHIONEIN ISOFORMS BY REVERSED-PHASE HPLC WITH ONLINE ION-SPRAY MASS-SPECTROMETRIC DETECTION

Microbore reversed-phase HPLC with on-line ion-spray mass spectrometri c detection is proposed for a study of polymorphism of rabbit liver me tallothionein (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 ion-spray 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 pe aks, whereas those of MT-1 and MT-2 showed nine and seven different pe aks, respectively. The on-line determination of the molecular masses ( +/-1 Da) of the compounds eluted permits the unambiguous cataloguing a nd further referencing of putative and true MT subisoforms. The result s 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 we re studied by HPLC with on-line ICP MS detection.