title: Gut pH as a limiting factor for digestive proteolysis in cultured juveniles of the gilthead sea bream (Sparus aurata).
abstract: After the development of the gastric function in juvenile fish, dietary proteins enter a two-phase digestive process comprising an acidic gastric phase followed by an alkaline intestinal phase. However, the main gastric protease, pepsin, is strictly dependent on the existence of a low-enough environmental pH. In 20-g gilthead sea bream, Sparus aurata, the mean minimal gastric pH is close to 4.5, while the mean pH in the duodenal portion of the intestine was nearly fixed at 6.5. The mean maximal gastric content of HCl was approximately 20 microEq for a low-buffering diet. Gastric proteases were more severely affected than intestinal proteases when assayed at actual sub-optimal pH values, 4.5 and 6.5, respectively. When the gastric proteases of juvenile fish were pre-incubated with a citric acid buffer at pH 6.0, the activity at pH 4.5 was very low, whereas when they were pre-incubated with the same buffer at pH 3.0, the activity at pH 4.5 was significantly increased; this fact suggests a deficient activation of zymogens during the gastric digestion and points to a potential approach to improve protein digestion in juvenile gilthead sea bream.
authors.affiliation: Departamento de Biología Aplicada, Escuela Politécnica Superior, Universidad de Almería, Almería, Spain. marquez.lorenzo728@gmail.com
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Márquez
authors.forename: Rocío
authors.initials: R
authors.lastname: Robles
authors.forename: Gabriel A
authors.initials: GA
authors.lastname: Morales
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Moyano
mesh_terms: D000821:Animal Feed; D000818:Animals; D004032:Diet; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism; D004063:Digestion / Q000502:physiology; D004064:Digestive System / Q000378:metabolism; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism; D005398:Fisheries; D005744:Gastric Acid / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D010447:Peptide Hydrolases / Q000378:metabolism; D059748:Proteolysis; D021541:Sea Bream / Q000502:physiology*
chemical_list: D004044:Dietary Proteins; D004792:Enzyme Precursors; D010447:Peptide Hydrolases
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