Distribution and Substrate Specificity of D-Amino Acid and D-Aspartate Oxidases in Marine Invertebrates

Abstract

The distribution of D-amino acid oxidase (DAO, EC 1.4.3.3) and D-aspartate oxidase (DDO, EC 1.4.3.1) activities was examined on several tissues of various marine invertebrate species. Only DAO activity was detected in kidney and midgut gland from most of the mollusks with some exceptions. Hepatopancreas or liver from kuruma prawn, crayfish, squid, and octopus and antenal gland from crayfish showed significant amount of activity of both enzymes. Squid demonstrated a higher activity of DDO than that of DAO. D-Proline was the best substrate for DAO in common flying squid liver followed by D-alanine, D-histidine, D-tyrosine, and D-phenylalanine. On the contrary, meso-2,3-diaminosuccinate was the best substrate for DDO followed by N-acetyl-DL-aspartate, D-glutamate, D-amino adipate, and D-homocysteic acid. These enzymes, at least in kidney and midgut gland, are believed to metabolize exogenous and endogenous free D-alanine, that is abundant in aquatic invertebrates such as crustaceans and bivalve mollusks.