Analytical approach to the metallomic of Nile tilapia (Oreochromis niloticus) liver tissue by SRXRF and FAAS after 2D-PAGE separation: Preliminary results

An investigation was made into calcium, iron and zinc in protein spots in samples of Nile tilapia (Oreochromis niloticus) liver tissue obtained after protein separation by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and subsequent qualitative and quantitative evaluation by synchrotron radiation X-ray fluorescence (SRXRF) and Flame Atomic Absorption Spectrometry (FAAS). An analysis of the fluorescence spectra indicated the presence of calcium, iron and zinc in 12, 6 and 8 liver protein spots, respectively. The metal ions found were distributed mainly in proteins with a molar mass of less than 40.00 kDa and more than 12.00 kDa, with pI in the range of 4.70–9.40. The only exception was a spot presenting protein with a molar mass of 10.10 kDa. In addition to calcium, iron and zinc, sulfur and phosphorus – which are non-metals that may be part of the protein structure, were also detected. After microwave-assisted acid mineralization of the proteins spots, a FAAS estimation of the concentration of calcium, iron and zinc ions bound to these proteins indicated a range of 1.08–5.80 mg g−1, 2.02–8.03 mg g−1 and 1.60–8.55 mg g−1, respectively.