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

Abstract

Anadara kagoshimensis (Tokunaga, 1906) is an invasive bivalve mollusk colonizing the Black Sea and Azov Sea. The content of 16 proteinogenic amino acids was determined in their hemolymph and soft tissue protein hydrolysates via ion-exchange chromatography followed by ninhydrin detection. High histidine and proline levels were detected both in hemolymph and in soft tissue hydrolysates. Experimental hypoxia caused qualitative and quantitative changes in the content of free amino acids, namely the pool of aliphatic amino acids decreased 2-fold, while the pool of aromatic amino acids conversely increased. It is assumed that the metabolism of A. kagoshimensis shifts under hypoxic conditions toward anaerobic catabolism of amino acids and proteins as a source of substrates for the tricarboxylic acid and ornithine cycles. This leads to a significant accumulation of arginine, which is an allosteric activator of ornithine cycle reactions, and urea, which is a low-molecular-weight (LMW) antioxidant. Thereby, an LMW component of the antioxidant defense system forms in A. kagoshimensis, as manifested in high levels of such free radical scavengers as histidine and urea, which may contribute to the invasion success of this alien bivalve species in the Black and Azov Seas.