Distribution and characteristics of D‐amino acid and D‐aspartate oxidases in fish tissues

Abstract

The distributions of D-amino acid oxidase (D-AAO, EC 1.4.3.3) and D-aspartate oxidase (D-AspO, EC 1.4.3.1) activities were examined on several tissues of various fish species. Both enzyme activities were commonly high in kidney and liver and low in intestine with some exceptions. After oral administration of D-alanine at 5 micromol /g body weight(-1)day(-1) to carp for 30 days, D-AAO activity increased by about 8-, 3-, and 1.5-fold in intestine, hepatopancreas, and kidney, respectively, whereas no increase was found in brain. In contrast, oral administration of D-glutamate or D-aspartate did not show any increase of D-AspO activity in any tissues. D-AAO and D-AspO of common carp kidney and hepatopancreas were subcellularly localized in peroxisomes, as clarified in mammals. D-proline was the best substrate for D-AAO in rainbow trout kidney, common carp kidney, and hepatopancreas, followed by D-alanine and D-phenylalanine. N-methyl-D-aspartate was the best substrate for D-AspO in rainbow trout kidney and common carp hepatopancreas. The optimal pH for D-AAO in rainbow trout kidney was broad, from 7.4 to 8.2, and that for D-AspO was around 10. D-AAO was inhibited by benzoate known as D-AAO inhibitor and D-AspO was strongly inhibited by meso-tartarate as D-AspO inhibitor. From these results, at least D-AAO in fish is considered to work as a metabolizing agent of exogenous and endogenous free D-alanine that is abundant in aquatic invertebrates such as crustaceans and bivalve mollusks, which are potential food sources of these fishes.

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“…DDO, on the other hand, oxidizes only dicarboxylic D-amino acids and their derivatives. Flying squid liver DAO demonstrated almost the same order of preference for substrate as DAO 16 found in rainbow trout kidney, common carp kidney and hepatopancreas. D-Proline was found the best substrate for mammalian DAO 24 .…”

“…The properties of DDO of Octopus vulgaris have been studied extensively 23 . Both of these enzyme activities are commonly high in kidney and liver and low in intestine of fish, and are believed to eliminate D-amino acids from fish tissues 16 . .…”

“…In spite of the extensive research on both enzymes in mammals and microorganisms, only a little information has been available for the other organisms including aquatic animals. Several results, however, have reported the presence of these enzymes in aquatic animals, such as the presence of both DAO and DDO in octopus 2,13 , and that of DDO in octopus 14 and in several fish species 15,16 . Although these enzymes were discovered 70 years ago 1 , their physiological function still remains unclear.…”

“…Information on the distribution and properties of these enzymes in aquatic animals would be useful in delineating the physiological function of the enzymes, because of the daily oral intake of Damino acids by aquatic animals. In our previous study, we investigated distribution pattern of these enzymes in fish 16 . In this study, we examined on the distribution of DAO and DDO in the tissues of various marine invertebrates.…”

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“…Moreover, certain D-amino acids play critical roles in regulating neural activities in vivo 3 . In contrast, the D-Amino acid oxidase (DAO, EC 1.4.3.3), a flavin adenine dinucleotide (FAD)-dependent and highly stereoselective flavoenzyme, occurs widely in microorganisms [4][5][6] and in animal tissues [7][8][9] . It is a marker enzyme of microbodies in yeast and peroxisomes of higher organisms 10 .…”