Some age features of biochemical adaptation to cadmium in scallop Mizuhopecten yessoensis

The scallop Mizuhopecten yessoensis is a Far Eastern representative of bivalve mollusks capable of accumulating cadmium in soft tissues without any visible pathological effect even in those habitats where cadmium does not exceed background values. This unique feature is caused by two MT-like Cd-binding proteins with the molecular mass of 72 and 43 kDa They present at least in the tissues of the digestive gland of adult M. yessoensis ( aged 5-7 years), one of the main organs accumulating heavy metals. As for 1-, 2-, 3-year-old scallops M. yessoensis, their mechanisms of adaptation to cadmium are unknown. At that, it is the age groups that mainly used in mariculture farms. Therefore, the aim of this work was to clarify the features of adaptation to cadmium in these age groups of the M. yessoensis. The scallops M. yessoensis were obtained from Severnaya Bay of the Northern part of the Peter the Great Bay of the Sea of Japan (42˚93 'N, 131˚40' E) and were transported to the laboratory of POI FEB RAS in Vladivostok. Then scallops were exposed to CdCl2 (300 µg/ml). To identify MT-like proteins, standard techniques for the isolation of MT from marine invertebrates and other necessary biochemical methods were used. As a result of the experiment on the accumulation of cadmium (300 μg/ml CdCl2), different age features of the accumulation of such metals as Cd, Zn and Cu by the digestive gland of M. yessoensis were found. It was stated that one-year-old scallops are able to bind cadmium to a greater amount than other investigated age groups. This feature is consistent with the presence of proteins with a molecular weight of 120 kDa in the digestive gland. Whereas in the two-years old scallops M. yessoensis this protein losses its binding function, and in 3-year old species its synthesis completely stops. On reaching maturity (3 years) the main cadmium-binding protein in the digestive gland of M. yessoensis becomes MT-like protein 72 kDa. Besides, it was found that in the two-year-old scallops a rearrangement of metabolism due to the transition to the mature stage occurred. We assume that due to this reason they do not bind cadmium in the amount close to 3-year old scallops. Total antioxidant capacity of Cd-binding proteins in 1-, 2- and 3-year-old scallops M. yessoensis was also studied. Thus, it was shown that the 1- and 3-years old individuals of M. yessoensis have a well-developed system of adaptation to cadmium. It is shown that these age groups are able to accumulate cadmium both in control conditions and when exposed to sea water with high cadmium content.