Katsuko Watanabe

Role of free d- and l-alanine in the Japanese mitten crab Eriocheir japonicus to intracellular osmoregulation during downstream spawning migration

Abstract Changes of d - and l -alanine and other osmolytes were examined in the tissues and hemolymph of the Japanese mitten crab Eriocheir japonicus captured during the maturation in the river and during the course of spawning migration downstream. Only d - and l -alanine and inorganic ions increased significantly in muscle during the maturation in freshwater from July to October and during downstream migration to estuaries in October. Inorganic ions in muscle was the highest in estuaries. In the crabs captured in the sea, glycine and d - and l -alanine were largely elevated in place of the inorganic ions declined. No other free amino acid increased in the muscle of the sea specimens. In hemolymph, total amino acids comprised only 4-10% of total osmolytes and decreased with maturation and during migration. Hemolymph inorganic ions were the highest also in estuaries. These data suggest that, in addition to a role as osmolyte, d - and l- alanine in the tissues of this strong hyperosmoregulator play an important role in the adjustment of salinity tolerance prior to and during downstream migration toward the sea.

Enhancing Effect of Nucleotides on Sweetness of Heated Prawn Muscle

Various kinds of prawns, lobsters, and shrimp are eaten raw or heated in Japan. However, most of the studies related to their taste and taste components focused on the raw muscle. Hujita et al. [1], who analyzed free amino acids in the raw muscles of nine kinds of prawns and lobsters, reported that their palatability is closely related to the total amount of sweet amino acids, such as glycine (Gly), proline, serine (Ser), and alanine (Ala), especially the amount of Gly. Take et al. [2] also examined the taste of aqueous extracts of dried shrimp (Sergestes lucens) and fresh prawn (Pandalus borealis). They treated the extracts with either glutamate decarboxylase or nucleotidase and noted that the disappearance of glutamate resulted in a slight decrease in umami, but that adenosine 5′-monophosphate (AMP) was not responsible for the taste. The taste components of prawns and lobsters have been reviewed by Konosu [3].