Comparison of two SH-based methods for estimation of metallothionein level in the digestive gland of naturally occurring mussels, Mytilus galloprovincialis

Abstract

Two methods for the evaluation of metallothionein (MT) level in Mytilus galloprovincialis digestive gland homogenate extract, polarographic and spectrophotometric, were compared in combination with sample subjected to heat treatment (at 70 and 85°C) as well as to solvent precipitation. Spectrophotometric measurements ranging within 0.081–0.144 mg MTg−1 were at least one order of magnitude lower in comparison with the polarographic ones (2.21–2.88 mg MTg−1) depending on the particular sample treatment as well as two specific reagents and reference standards applied.Sephadex G-75 column chromatography of the differently treated samples and subsequent polarographic analysis in the pooled elution fractions indicated that a level of nonMT interfering thiolic component in homogenate extract may be accounted for more than 50% of the total polarographic signal, irrespective of a method o sample treatment applied. Consequently, the large discrepancy between methods could not be attributed only to the sample treatment procedures but more likely to certain not entirely explained analytical problems, particularly calibration with appropriate reference standard.