[2022 AWARD WINNING PAPER] Red-spotted grouper Epinephelus akaara blood L-amino acid oxidase utilizes the substrates in plasma

2022 Award of Excellence for the Science Papers

Fish Sci (2022) 88:635–643
DOI: https://doi.org/10.1007/s12562-022-01617-x


Yoichiro Kitani


L-amino acid oxidases (LAOs) oxidatively deaminate L-amino acids and generate H2O2. Recently, a novel LAO was isolated from the red-spotted grouper Epinephelus akaara serum (EaLAO) and it showed antibacterial activity via H2O2. The enzymatic activity of EaLAO was normally suppressed in blood and was activated by mixing it with seawater. This phenomenon suggested that EaLAO may stand by as an inactive form in the body, and it functions as an antibacterial protein at the bleeding trauma sites. For pathogen protection by EaLAO at the wound site, instant H2O2 production is essential. In this work, the substrate source of EaLAO and the H2O2-generation potential of the grouper plasma were studied. Mixing plasma with seawater or cations generated 0.26–0.48 mM of H2O2 except for the addition of L-amino acid substrates. The amino acid quantification of plasma via fluorescent HPLC showed that the alanine was dominantly consumed after being mixed with seawater. The VmaxKm, and turnover number of EaLAO with L-alanine at 25 °C in seawater were 1618 μU/reaction, 86.6 mM, and 10.6 s−1, respectively. Furthermore, Vibrio harveyi was 84% killed by the plasma–seawater mixture. These results suggested that L-alanine may be the primary substrate of EaLAO in plasma.


L-amino acid oxidase (LAO) / Epinephelus akaara / Substrate amino acids / Plasma

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