Component of several enzyme complexes such as the branched chain a-keto acid dehydrogenase involved in the catabolism of leucine, isoleucine and valine. Cystathionine gamma-lyase was upregulated and is involved in the last step in the trans-sulfuration pathway from methionine to cysteine and can be both involved in the degradation of methionine and cysteine. Finally, upregulated glutamate dehydrogenase 1 is involved in the biosynthesis or catabolism of glutamate and catalyzes the oxidative deamination of glutamate to 2-ketoglutarate which is an important intermediate in the TCA cycle. The observed increase in amino acids catabolism may be necessary to compensate for the lack of energy available caused by the embryonic undernutrition. As the albumen removal decreased the protein availability at the end of the incubation, changes in the expression of enzymes involved in amino acid metabolism could be foreseen. Indeed, a previous study also found indications of an altered protein metabolism in broilers treated by albumen removal before incubation, suggesting a transient increase in muscle proteolysis. Metabolic programming caused by prenatal protein undernutrition was revealed by the observed hepatic proteome changes related with glucose metabolism. Upregulation of L-lactate dehydrogenase B chain suggests an increased conversion of pyruvate to lactate in the absence of oxygen in the liver. This lactate can subsequently be converted to glucose by the gluconeogenesis. Two of the regulatory enzymes of the latter pathway were dysregulated in the liver. Fructose-1,6-biphosphatase 1 was downregulated, whereas phosphoenolpyruvate 2 was upregulated. FBP1 catalyzes the conversion of D-fructose-1,6-biphosphate to D-fructose-6-phosphate, whereas PCK2 catalyzes the conversion of oxaloacetate to phosphoenolpyruvate, the rate-limiting step. Upregulated a-enolase is also involved in both the gluconeogenesis and glycolysis and catalyzes the conversion of 2-phospho-D-glycerate to phosphoenolpyruvate. In addition, glucose transporter 1, a facilitative low capacity/high affinity glucose transporter across the plasma membrane was upregulated. Hepatic GLUT1 is primarily involved in cellular uptake of glucose from the plasma into the hepatocytes when nutrients are in reduced supply. As no differences in plasma glucose or lactate levels were found, it is not clear whether the gluconeogenesis pathway in general is up- or downregulated. Furthermore, a general upregulation of the TCA pathway was observed, from the upregulation of several enzymes involved such as DLD, aconitate hydratase and malate dehydrogenase 1. DLD is a component of the pyruvate dehydrogenase complex, which converts pyruvate, originating from the breakdown of carbohydrates to acetyl-CoA, the input for the TCA cycle. ACO2 catalyzes the isomerization of citrate to isocitrate via cis-aconitate, and MDH1 the conversion of malate to oxaloacetate.