The effect of protein and methionine intake on glutamate dehydrogenase and alanine aminotransferase activities in juvenile black tiger shrimp Penaeus monodon Lenaïg Richard a,b, ⁎, Christiane Vachot a , Jeanine Brèque a , Pierre-Philippe Blanc b , Vincent Rigolet b , Sadasivam Kaushik a , Inge Geurden a a INRA, UMR1067 Nutrition, Aquaculture and Genomics, F-64310 Saint-Pée-sur-Nivelle, France b AQUALMA, BP 93 Immeuble SCIM, 4 rue Galliéni, Mahajanga 401, Madagascar abstract article info Article history: Received 15 March 2010 Received in revised form 17 June 2010 Accepted 18 June 2010 Keywords: ALAT Amino acid catabolism Crustaceans Dietary protein level GDH Indispensable amino acids This study evaluates the influence of both dietary protein and methionine on amino acid trans- and deamination (alanine aminotransferase, ALAT and glutamate dehydrogenase, GDH) in three tissues (muscle, hepatopancreas, gills) of the marine black tiger shrimp (Penaeus monodon). Shrimp (2.4 g) were fed one of the six semi-purified diets containing 14, 34 or 54% crude protein (% dry matter) with two levels of methionine (normal or 30% reduced) for 6 weeks. Both ALAT and GDH activities were the highest in the muscle. ALAT activity in muscle significantly decreased when feeding the low vs. high protein diets. Compared to those fed the intermediate protein level, GDH activity in muscle decreased (by 35%) when fed the low and increased (by 26%) when fed the high protein diets (P b 0.05). A significant interaction between dietary protein and methionine was observed on GDH activity in gills which, due to the relative methionine deficiency, increased 4-fold at the intermediate protein level. In summary, our results demonstrate for the first time the capacity of up and downregulation of enzyme activity by dietary protein levels in the muscle of P. monodon, and the active role played by branchial tissue in ammoniogenesis in response to a relative indispensable amino acid (methionine) deficiency. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Despite its importance in aquaculture as the second most cultured marine shrimp species worldwide (FAO, 2007), data on protein and amino acid (AA) metabolism are limited in the black tiger shrimp, Penaeus monodon. In natural conditions, P. monodon is known to have a predator- like feeding behaviour (Marte, 1980). This has been highlighted by the high protein requirement (23.9 g protein kg -1 BW/d) found in our earlier study of which 20% was used for maintenance (Richard et al., 2010). In the same study, methionine requirement for optimal N gain was found to be 2.9% of crude protein (CP), which agrees well with previous estimations of 2.4% CP for P. monodon postlarvae (Millamena et al., 1996). Furthermore, using a broken line regression, marginal efficiency of N utilisation (between maintenance and optimal growth) for N gain was found to be only 24%, whereas total N retentions (N gain/N intake) ranged between 11 and 17% (Richard et al., 2010). Other studies on crustacean shrimp species similarly reported relatively low N retentions, comprised between 10 and 15% for Litopenaeus stylirostris (Gauquelin et al., 2007) or around 20% for P. monodon reared in intensive commercial conditions (Briggs and Funge- Smith, 1994; Jackson et al., 2003). These results imply the loss of a significant portion of the ingested nitrogen into the environment, which is not used for body protein accretion. In decapod crustaceans, ammonia is the main form of metabolic N excretion (Regnault, 1987). The identified pathways for AA degradation in crustaceans are generally considered to correspond to those of vertebrates (Claybrook, 1983). The detection of both alanine aminotransferase (ALAT, EC 2.6.1.2) and glutamate dehy- drogenase (GDH, EC 1.4.1.3) in several crustacean species (Claybrook, 1983; Mayzaud and Conover, 1988; Chien et al., 2003; Li et al., 2009) supports this idea. While ALAT enables the transamination of AA, GDH plays a central role in the flux of ammonia in the free AA pool as it catalyses the transformation of glutamate into ketoacid and ammonia and vice versa (Greenaway, 1991). It was initially believed that only the reductive function leading to glutamate synthesis occurred in crustacea (Claybrook, 1983). However, later studies (Batrel and Regnault, 1985; King et al., 1985; Regnault, 1987; Greenaway, 1991) have demonstrated also the oxidative function of GDH, underlining the central role of GDH in crustaceans as in other species not only in ammonia uptake but also in ammonia production. Most studies on the activities of ALAT (Galindo-Reyes et al., 2000; Chien et al., 2003; Pan et al., 2003) or GDH (Regnault, 1987; Rosas et al., 2001) in crustaceans have dealt with the effect of environmental factors (salinity, ambient ammonia) on free AA metabolism (osmoregulation, ammonia detoxification). Only few have documented the effect of Journal of Experimental Marine Biology and Ecology 391 (2010) 153–160 Abbreviations: AA, Amino acid; ALAT, Alanine aminotransferase; CP, Crude protein; Cys, Cystine; GDH, Glutamate dehydrogenase; IAA, Indispensable amino acid; Met, Methionine; N, Nitrogen; Shr, Shrimp; TFAA, Total free amino acids. ⁎ Corresponding author. INRA, UMR1067 Nutrition, Aquaculture and Genomics, F-64310 Saint-Pée-sur-Nivelle, France. Tel.: +33 559515963; fax: +33 559545152. E-mail address: lrichard@st-pee.inra.fr (L. Richard). 0022-0981/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2010.06.024 Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe