Scientific and Educational Reports of the Faculty
of Science and Technology, Kochi University
Vol. 5 (2022), No. 4
Ryoko Shouno，Tomohiko Suzuki
Faculty of Science & Technology, Kochi University, Kochi 780-8520, Japan
Abstract
A small shrimp, Neocaridina denticulata survives in a wide temperature range of 1-30°C. In the previous report, we showed that the shrimp expresses two types of arginine kinases, AK1 and AK2, which were identified as psychrophilic and mesophilic enzyme, respectively, by the criterion of the activation energy (Ea) and thermodynamic values of Δ(ΔHo‡)p-m and Δ(TΔSo‡)p-m. We searched DNA database using the sequence of psychrophilic AK1 as a query, and identified nine AK sequences (8 from Arthropod and one from Ctenophora). All the nine sequences, including Neocaridina AK1, had a unique amino acid sequence of QHC at positions 85-87, instead of SGV sequence conserved widely in most of AKs including mesophilic Neocaridina AK2 and associated with the binding sites of the substrate arginine. Among the nine sequences, we cloned and expressed three AKs from the brackish-water calanoid copepod Pseudodiaptomus annandalei, the salmon louse Lepeophtheirus salmonis and the Antarctic krill Euphausia superba. The three enzymes showed guanidino substrate specificity only for L-arginine, and the complete kinetic constants of the AK reaction were determined for the former two AKs. In addition, the apparent kcatARG or ATP and KmARG or ATP values of Pseudodiaptomus and Lepeophtheirus AKs were determined under 4.76 mM ATP or 4.76 mM arginine, respectively, at six to seven different temperatures between 15 to 30°C. The activation energy (Ea) and thermodynamic parameters for the transition state of AK reactions suggested that Pseudodiaptomus and Lepeophtheirus enzymes were psychrophilic. The present results indicate that psychrophilic AKs may be widespread in crustacean groups.
Received: February 14, 2022
Reviewed by anonymous referee(s), and accepted: February 20, 2022
Published: March 29, 2022
発行者：高知大学理工学部 〒780-8520 高知県高知市曙町二丁目5-1
Faculty of Science and Technology, Kochi University, Kochi, 780-8520 Japan
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