Distribution of D-Amino acids in Aquatic Animals

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D-amino acids are generally viewed as natural oddities. However, recent investigations show a rather wide distribution of some D-amino acids in microbes, plants and higher animals. The present studies were planned to accumulate more information on the distribution of D-enantiomer of alanine in aquatic animals.Eighty percent ethanol extracts were prepared from tissues of 37 species in 5 phyla (Mollusca, Arthropoda, Echinodermata, Prochordata, and Vertebrata). The concentration of D-alanine in the extracts was determined in two different ways: 1) measuring alanine in the extract before and after incubation with D-amino acid oxidase (EC 1.4.3.3) by an amino acid autoanalyzer and 2) analyzing as trifluoroacetyl 1-propyl derivatives of alanine by gas chromatography on a capillary column of chiracil-Val.Significant amounts of D-alanine (150-820 mg, The concentration of D-alanine is expressed in terms of mg per 100 g of tissue.) were detected in the muscles of some marine bivalves such as Mac … More tra chinensis, Spisura sachalinensis, Tresus keenae, Peronidia venulosa, and Meretrix lusoria but not in the muscles of marine bivalves such as Amusium Japonicum, Scapharca broughtonii, Patinopecten yessoensis, Atrina pectinata, and Ostrea edulis. In all the D-alanine-containing species, the concentration of D-alanine was much higher than that of L-isomer. Forty one mg of D-alanine was also found in the soft part of a brackish bivalve Corbicula leana. It is noteworthy that D-alanine-containing bivalves belong to the order Heterodonta and D-alanine-lacking bivalves to the order Pteriomorphia. No measurable quantity of D- alanine could be detected in gastropods and cephalopods. In the muscles of all the crustacean species analyzed, D-alanine was found. The level of the amino acid was variable, ranging from 10 mg in Homarus americanus to 260 mg in Eriocheir sinensis, although concentration ratio of D-alanine to total alanine (D/D+L) was between 0.3 and 0.4. Sizable amount of the amino acid was detected in the gonad of both species of sea urchins Hemicentrotus pulcherrimus (90 mg) and Anthrocidaris crassispina (170 mg) and their D/D+L ratios were 0.72 and 0.47, respectively. The muscle of ascidian Halocynthia roretzi and five species of fishes did not contain D-alanine. Less