Patterns of catabolic capacities and energy metabolism in developing embryos and yolk-sac larvae of turbot (Scophthalmus maximus L.).

Patterns of catabolic capacities and energy metabolism in turbot eggs during embryogenesis and yolk-sac larvae were investigated. The catabolization of energy fuels were evaluated by specific enzymes including trypsin-like proteases (TRY) for protein and triglyceride lipase (LIP) for lipids. Meanwhile, citrate synthase (CS) and lactate dehydrogenase (LDH) were measured to assess energy production pathway. Regarding contribution to energy production, the enzymes of pyruvate kinase (PK), aspartate aminotransferase (AAT) and hydroxyacyl CoA dehydrogenase (HOAD) which was indicative of the mobilizations of carbohydrates, amino acids and fatty acids respectively and their ratios were detected. Results showed the metabolic enzymes and catabolic enzymes were present and involved in the embryogenesis of turbot. LIP activity exhibited a pattern of ‘low-high-low-high’. TRY activity dropped to the minimal value at blastula stage, and then increased significantly to the maximal value at 2 days after hatching (DAH). The enzymatic activities of HOAD, AAT, LDH and CS all showed similar upward tendency and increased significantly as development went on. PK activity increased to the peak at cleavage stage, and then decreased to the lowest point at hatching day. Concerning enzymatic ratios, both AAT/HOAD and PK/HOAD presented similar “high-low” patterns, showing the maximal value 3.18 and 45.27 respectively at cleavage stage and the minimal value 0.46 and 0.84 respectively at 2 DAH. PK/AAT ratio declined from fertilized eggs (14.31) to 2 DAH (1.82). PK/CS ratio decreased significantly from cleavage stage (1.63) to 2 DAH (0.16). In contrast, a rising tendency of HOAD/CS ratio appeared as growth went on. AAT/CS ratio peaked at gastrula stage (0.13) and declined thereafter. LDH/CS ratio increased from fertilized eggs (1.42) to cleavage stage (1.85), and then decreased until 2 DAH (0.55). LDH/PK ratio reached the peak of 3.85 at hatching day. Combined with patterns of enzymatic ratios, it can be concluded that carbohydrates are predominantly mobilized before cleavage stage and are gradually substituted by amino acids from cleavage stage to gastrula stage and fatty acids during the following days, revealing their importance for morphogenesis in turbot. Regarding energy production pathway, the dominant mode was anaerobic pathway before cleavage stage and aerobic pathway during subsequent periods. [ABSTRACT FROM AUTHOR]