Effect of Hypoxia on Amino Acid Content in Hemolymph and Protein Hydrolysate of the Bivalve Mollusk Anadara kagoshimensis

Anadara kagoshimensis (Tokunaga,1906) is an invasive bivalve mollusk colonizing the Black Sea andAzov Sea. The content of 16 proteinogenic amino acids was determinedin their hemolymph and soft tissue protein hydrolysates via ion-exchangechromatography followed by ninhydrin detection. High histidine andproline levels were detected both in hemolymph and in soft tissuehydrolysates. Experimental hypoxia caused qualitative and quantitativechanges in the content of free amino acids, namely the pool of aliphaticamino acids decreased 2-fold, while the pool of aromatic amino acids converselyincreased. It is assumed that the metabolism of A. kagoshimensis shifts under hypoxic conditionstoward anaerobic catabolism of amino acids and proteins as a sourceof substrates for the tricarboxylic acid and ornithine cycles. Thisleads to a significant accumulation of arginine, which is an allostericactivator of ornithine cycle reactions, and urea, which is a low-molecular-weight(LMW) antioxidant. Thereby, an LMW component of the antioxidantdefense system forms in A. kagoshimensis,as manifested in high levels of such free radical scavengers ashistidine and urea, which may contribute to the invasion successof this alien bivalve species in the Black and Azov Seas.