Hepatic phosphoenolpyruvate carboxykinase gene expression is not repressedby dietary carbohydrates in rainbow trout (Oncorhynchus mykiss)

Phosphoenolpyruvate carboxykinase (PEPCK) is a rate-limiting enzyme in hepa tic gluconeogenesis and therefore plays a central role in glucose homeostas is. The aim of this study was to analyse the nutritional regulation of PEPC K gene expression in rainbow trout (Oncorhynchus mykiss), which are known t o use dietary carbohydrates poorly. A full-length hepatic PEPCK cDNA (2637 base pairs with one open reading frame putatively encoding a 635-residue pr otein) was cloned and found to be highly homologous to mammalian PEPCKs. Th e presence of a putative peptide signal specific to a mitochondrial-type PE PCK in the deduced amino acid sequence suggests that this PEPCK gene codes for a mitochondrial form, In gluconeogenic tissues such as liver, kidney an d intestine, this PEPCK gene was expressed at high levels and, in the liver we found no regulation of PEPCK gene expression by dietary carbohydrates. These results suggest that the first step of the hepatic gluconeogenic path way in rainbow trout is functional and highly active irrespective of the di etary carbohydrate supply.