Characterization of high molecular weight cadmium species in contaminated vegetable food

Spinach and radish grown from seeds were each contaminated with 4 different amounts of cadmium. After a cell breakdown of the eatable parts and centri fugation of the resulting homogenates all supernatants (cytosols) were sepa rated by gel permeation chromatography (GPC). The size-range of the GPC met hod used was about 20-8000 kDa for globular proteins. The high molecular we ight (HMW-Cd-SP, 150-700 kDa) and the low molecular weight Cd species (LMW- Cd-SP, < 150 kDa) in all plant cytosols eluted at about the same retention volume by GPC. The most important Cd binding form in the cytosols of all pl ants was found to be HMW-Cd-SP. The Cd elution maxima were detected in the range of about 200 kDa. The Cd determinations were performed with ET-AAS by means of matrix modifier. By incubating chosen cytosols with a proteinase before the GPC it was verified that the HMW-Cd-SP in both vegetables are Cd proteins. The molar proportions protein/Cd were about 2-6 in the respectiv e GPC fractions of the HMW-Cd-SP of the highest contaminated plants. The GP C fractions of the HMW-Cd-SP of spinach and radish were further separated b y a preparative, native and continuous polyacrylamide gel electrophoresis ( PAGE) method. At pH 8 the species were negatively charged, had only a small UV-absorption at 280 nm and showed a very similar elution behavior in all analyzed cytosols. Therefore, we suppose that the HMW-Cd-SP of these two di fferent vegetable foodstuffs have a very similar chemical structure.