Fatty acid synthesis in chick embryonic heart and liver during development

Abstract

Fatty acid synthesis by subcellular fractions of heart and liver of chick embryos at varying stages of development has been studied. Fatty acid synthetase activity is associated with the embryonic heart at early stages of development, as suggested by substrate requirement, Schmidt decarboxylation of synthesized fatty acids and gas liquid chromatographic identification of the products as palmitic and stearic acids. The fatty acid synthetase activity decreases in heart cytosol with age of the embryo and is absent in the newly hatched chick and in older chicken. The acetyl CoA carboxylase activity is negligible in embryonic and adult chicken heart. The fatty acid synthetase activity in liver is low, but measurable during the entire embryonic development. The activity increases by about three-fold on hatching and thereafter in fed, newly hatched chicks by about 35-fold, over the basal embryonic activity. The acetyl and malonyl transacylase activities in the heart and liver cytosols during development followed closely the fatty acid synthetase activities in heart and liver, respectively. A non-coordinate induction of fatty acid synthetase and acetyl CoA carboxylase activities in liver was observed during development. The microsomal chain elongation in liver and heart followed the pattern of fatty acid synthetase activity in liver and heart, respectively. The mitochondrial chain elongation in embryonic heart is initially low and increases with age; while this activity in liver is higher in early stages of embryonic development than in the older embryos and the chicks. Measurement of lipogenesis from acetate-1- 14C by liver and heart slices from chick embryos and newly hatched chicks support the conclusions reached in the studies with the subcellular fractions. The results obtained indicate that the major system of fatty acid synthesis in embryonic and adult heart is the mitochondrial chain elongation. In embryonic liver, fatty acid synthesis proceeds by chain elongation, while the de novo system is the major contributor to the lipogenic capacity of the liver after hatching.