Phosphoenolpyruvate carboxykinase cytosolic and mitochondrial isoforms are expressed and active during hypoxia in the white shrimp Litopenaeus vannamei

Hypoxic zones in marine environments are spreading around the world affecting the survival of many organisms. Marine animals have several strategies to respond to hypoxia, including the regulation of gluconeogenesis. Phosphoenolpyruvate carboxykinase (PEPCK) is a key regulatory enzyme of gluconeogenesis. The objective of this work was to study two isoforms of PEPCK, one mitochondrial (PEPKC-M) and one cytosolic (PEPCK-C), from the white shrimp Litopenaeus vannamei and the response to hypoxia. Both PEPCK isoforms are 72 kDa proteins and have 92% identity at the amino acid level. The mitochondria] isoform has a N-terminal signal peptide for mitochondria] import. Gene expression and enzymatic activity in subcellular fractions were detected in gills, hepatopancreas and muscle in normoxic and hypoxic conditions. Expression of PEPCK-C was higher than PEPCK-M in all the tissues and induced in response to hypoxia at 48 h in hepatopancreas, while the enzymatic activity of PEPCK-M was higher than PEPCK-C in gills and hepatopancreas, but not in muscle and also increased in response to hypoxia in hepatopancreas but decreased in gills and muscle. During limiting oxygen conditions, shrimp tissues obtain energy by inducing anaerobic glycolysis, and although gluconeogenesis implies energy investment, due to the need to maintain glucose homeostasis, these gluconeogenic enzymes are active with contrasting behaviors in the cytosol and mitochondrial cell compartments and appear to be up-regulated in hepatopancreas indicating this tissue pivotal role in gluconeogenesis during the response to hypoxia.