Enzymes of Arginine Metabolism in the Scorpion Palamneus phipsoni: Presence of a Partial Urea Cycle and Conversion of Arginine to Proline and Glutamate

Scorpion (Palamneus phipsoni) tissues were assayed for the activities of the enzymes of the urea cycle and arginine catabolism. In the hepatopancreas, appreciable levels of arginase and ornithine carbamoyltransferase were present, but arginine synthetase activity could not be detected. None of the three enzymes was found in claw muscle and telson. The results suggest that a functional urea cycle is absent in this guanotelic species. Ornithine aminotransferase, Δ¹-pyrroline-5-carboxylate dehydrogenase, Δ¹-pyrroline-5-carboxylate reductase, and proline oxidase, which catalyze the interconversions of ornithine, glutamate, and proline, were present in scorpion tissues. The metabolic significance of these results has been evaluated in relation to arginine nutrition and ornithine catabolism in the scorpion.