Characterization of Alanine-Glyoxylate Aminotransferase 1 from Kuruma Shrimp Penaeus Japonicus and Its Gene Expression Profiles in Response to Different Salinities

Shrimps regulate osmotic pressure by altering the amounts of free amino acids in their bodies. While changes in alanine (Ala) content are particularly significant, the molecular mechanisms involved in controlling Ala levels remain largely unknown. In the present study, we investigated alanine-glyoxylate aminotransferase 1 (AGT1), an l-Ala-degrading enzyme, using the kuruma shrimp Penaeus japonicus as a model to elucidate the regulatory mechanism of l-Ala levels in shrimps. We found that kuruma shrimp AGT1 is specialized for l-Ala degradation and does not catalyze the reverse reaction. Its optimum pH and temperature were approximately 8.0–9.0 and 50 ºC, respectively, which are similar to those reported for AGT1s from other species. Structural analyses revealed that the amino acid residues constituting the active site were conserved, and the predicted three-dimensional structure was similar to that of known AGT1s. Investigation of AGT1 gene expression in kuruma shrimp acclimated to different salinities showed that its expression level in the abdominal muscle was low and did not fluctuate significantly. This result suggests that AGT1 plays a minor role in the regulation of l-Ala content in the abdominal muscle of kuruma shrimp, implying the existence of other primary regulatory mechanisms in this tissue.