Effect of hypoxia on amino acid content in haemolymph and protein hydrolysate of the bivalve mollusk Anadara kagoshimensis (Tokunaga, 1906)

Abstract

Anadara kagoshimensis (Tokunaga, 1906) is a bivalve alien species of the Black Sea and of the Azov Sea. The amino acid composition of hemolymph and protein hydrolysates of the mollusc soft tissues was studied. The content of 16 proteinogenic amino acids in the samples was determined by ion-exchange chromatography followed by ninhydrin detection. High concentrations of histidine and proline were observed in the hemolymph and soft tissues of the mollusc. Experimental hypoxia revealed qualitative and quantitative changes in the content of free amino acids in both hemolymph and soft tissue hydrolysates. In particular, the pool of aliphatic amino acids decreased twice and the pool of aromatic amino acids increased. The mass fraction of soft tissues almost halved under hypoxia, compared to normal conditions, which corresponded to 4.7% in the experiment and 8.2% in the control. This leads to a deterioration of the hydrolysates in total and amine nitrogen as well as in dry matter (0.34 and 1.84% of dry matter in hypoxia and normoxia). It has been shown that the metabolism of molluscs is reorganized under hypoxic conditions towards anaerobic catabolism of amino acids and proteins as a source of substrates for the citric acid and ornithine cycles. This leads to a significant accumulation of arginine, which is an allosteric activator of ornithine cycle reactions, and an accumulation of urea, which is a low-molecular-weight antioxidant. Thus, a low-molecular-weight part of the antioxidant defense system in the form of a high content of free radical scavengers like histidine and urea is formed in A. kagoshimensis, which may contribute to the success of the invasion of this mollusc in the Black Sea and of the Azov Sea. The issues of the influence of hypoxia on the quality of shellfish as raw materials for obtaining dietary supplements are considered.