Partial characterisation and distribution of kynurenine aminotransferase activity in the Black Tiger prawn ( Penaeus monodon)

• Published in: Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology 1998, Vol.120 (1), p.139-143
• Main Authors: Meunpol, Oraporn, Hall, Michael R, Kapoor, Vimal
• Format: Article
• Language: English
• Subjects: 3-Hydroxykynurenine; Brackish; Crustacean; Kynurenine; Kynurenine aminotransferase; Marine; Moulting; Penaeus; Penaeus monodon; Prawn; Xanthurenic acid
• ISSN: 1096-4959; 0305-0491; 1879-1107
• DOI: 10.1016/S0305-0491(98)10002-0

Xanthurenic acid, the product of the enzyme kynurenine aminotransferase, has been suggested to have significant moult inhibiting action in crustaceans. We investigated kynurenine aminotransferase activity and its distribution in the prawn, Penaeus monodon, using an enzyme assay based on the conversion of kynurenine to kynurenic acid, another activity associated with this enzyme. Kynurenine aminotransferase was most active at pH 8, and at 45°C with a substrate concentration of 10 mM kynurenine. Kinetic analysis showed apparent K m values of 0.25±0.06 mM for kynurenine and V max of 97±4 nM h −1 mg −1 protein. The enzyme activity was highest in cerebral ganglion followed by haemolymph, and only trace activity was detectable in thoracic ganglia, abdominal ganglia, hepatopancreas, heart, eyestalk and muscle. Kynurenine aminotransferase activity varied with the moult stage: that is, intermoult prawns had higher kynurenine aminotransferase activity than prawns in premoult or postmoult. Furthermore, larger, older prawns had significantly higher enzyme activity than younger prawns. These results are consistent with the hypothesis that xanthurenic acid, the endogenous product of kynurenine aminotransferase activity, may be important in the regulation of the crustacean moult cycle.