RESUMO
As other spiny lobsters, Panulirus argus is supposed to use preferentially proteins and lipids in energy metabolism, while carbohydrates are well digested but poorly utilized. The aim of this study was to evaluate the effect of dietary carbohydrate level on digestion and metabolism in the spiny lobster P. argus. We used complementary methodologies such as post-feeding flux of nutrients and metabolites, as well as measurements of α-amylase expression and activity in the digestive tract. Lobsters readily digested and absorbed carbohydrates with a time-course that is dependent on their content in diet. Lobster showed higher levels of free glucose and stored glycogen in different tissues as the inclusion of wheat flour increased. Modifications in intermediary metabolism revealed a decrease in amino acids catabolism coupled with a higher use of free glucose as carbohydrates rise up to 20%. However, this effect seems to be limited by the metabolic capacity of lobsters to use more than 20% of carbohydrates in diets. Lobsters were not able to tightly regulate α-amylase expression according to dietary carbohydrate level but exhibited a marked difference in secretion of this enzyme into the gut. Results are discussed to highlight the limitations to increasing carbohydrate utilization by lobsters. Further growout trials are needed to link the presented metabolic profiles with phenotypic outcomes.
RESUMO
Alpha-amylases are ubiquitously distributed throughout microbials, plants and animals. It is widely accepted that omnivorous crustaceans have higher α-amylase activity and number of isoforms than carnivorous, but contradictory results have been obtained in some species, and carnivorous crustaceans have been less studied. In addition, the physiological meaning of α-amylase polymorphism in crustaceans is not well understood. In this work we studied α-amylase in a carnivorous lobster at the gene, transcript, and protein levels. It was showed that α-amylase isoenzyme composition (i.e., phenotype) in lobster determines carbohydrate digestion efficiency. Most frequent α-amylase phenotype has the lowest digestion efficiency, suggesting this is a favoured trait. We revealed that gene and intron loss have occurred in lobster α-amylase, thus lobsters express a single 1830 bp cDNA encoding a highly conserved protein with 513 amino acids. This protein gives rise to two isoenzymes in some individuals by glycosylation but not by limited proteolysis. Only the glycosylated isoenzyme could be purified by chromatography, with biochemical features similar to other animal amylases. High carbohydrate content in diet down-regulates α-amylase gene expression in lobster. However, high α-amylase activity occurs in lobster gastric juice irrespective of diet and was proposed to function as an early sensor of the carbohydrate content of diet to regulate further gene expression. We concluded that gene/isoenzyme simplicity, post-translational modifications and low Km, coupled with a tight regulation of gene expression, have arose during evolution of α-amylase in the carnivorous lobster to control excessive carbohydrate digestion in the presence of an active α-amylase.
Assuntos
Proteínas de Artrópodes , Carnivoridade/fisiologia , Regulação Enzimológica da Expressão Gênica/fisiologia , Palinuridae , alfa-Amilases , Animais , Proteínas de Artrópodes/biossíntese , Proteínas de Artrópodes/genética , DNA Complementar/genética , DNA Complementar/metabolismo , Glicosilação , Isoenzimas/biossíntese , Isoenzimas/genética , Palinuridae/genética , Palinuridae/metabolismo , Proteólise , alfa-Amilases/biossíntese , alfa-Amilases/genéticaRESUMO
Detailed examination of early development and growth of Cuban gar (Atractosteus tristoechus) was conducted using morphologic and morphometric characters. Larvae were reared at a constant water temperature (28 ± 1°C) from hatching to 18 days after hatching (DAH). Observation of the disappearance, reduction, or appearance of external structures, pigment characteristics, and behavior, identified three developmental stages (attached 0-3 DAH; transitional 4-10 DAH; and free-swimming 11-18 DAH). For the 18 day trial, the average growth rate was 1.30 mm/d and the specific growth rate averaged 10.2%/d. The slowest growth rates (0.02 mm/d and 2.8%/d, 7-11 DAH) coincided with the exhaustion of yolk reserves and the transition from endogenous to exogenous feeding. In addition to the slowest growth rates, the most dramatic morphological changes in A. tristoechus were observed during the transition from endogenous to exogenous feeding. Five total length (TL) groupings were established using 25 morphologic and morphometic characters. The characters snout length, pelvic fin length, snout width at nares, head length, and head width best identified length groupings. As the larvae developed, the snout and head lengthened and narrowed. Proportionally, the snout was narrower and the head longer in Cuban gar larvae than in other lepisosteid larvae.