PATHWAYS OF SERINE AND GLYCINE METABOLISM IN PRIMARY CULTURE OF OVINEFETAL HEPATOCYTES

Previous in vivo studies in the ovine fetus have demonstrated net seri ne production by the fetal liver, a pattern not seen in the adult shee p. The goal of this study was to determine the major metabolic pathway s responsible for fetal hepatic serine production by using stable isot ope methodology in primary culture of late gestation ovine fetal hepat ocytes. Specifically selected tracers of glycine were added to individ ual cultures, with production of labeled serine determined after 24 h of incubation. When [1-C-13(1)]glycine or [2-C-13(1)]glycine was used as the initial tracer, serine enrichment at 24 h indicated that approx imately 30% of serine production comes from glycine. Quantitative comp arison of serine enrichment from these two tracers suggests that serin e synthesis from glycine occurs via the combined action of the glycine cleavage enzyme system (GCE) and serine hydroxymethyltransferase (SHM T). Using [1,2-(C2N1)-C-13-N-15]glycine as the tracer, there was no si gnificant increase in M+2 glycine in the medium over 24 h, suggesting no reversible transamination of glycine, and therefore no significant movement of glycine through the glyoxalate pathway. These data demonst rate that in primary culture of fetal ovine hepatoctyes, approximately 30% of serine biosynthesis is derived from glycine, primarily via the combined action of GCE and SHMT.