TISSUE LOCALIZATION OF THREONINE OXIDATION IN PIGS

Two experiments were designed to determine the tissue distribution of threonine oxidation through the threonine dehydrogenase (EC 1.1.1.103) pathway in pigs. The first experiment was conducted on eleven Pietrai n x Large White piglets. The piglets were slaughtered at 5, 12 or 20 k g after 1 h of infusion with L-[U-C-14]threonine (55 kBq/kg) mixed wit h unlabelled threonine (100 mg/kg). In the second experiment, four Pie train x Large White and four Large White piglets (10 kg body weight) w ere infused with L-[1-C-13]threonine (50 mg/kg) mixed with 50 mg/kg un labelled threonine for 1 h, then killed for tissue sampling. In the tw o experiments, threonine dehydrogenase specific activity and threonine and glycine specific radioactivities and enrichments were measured in several tissues and in plasma. The higher level of labelling of threo nine in the pancreas than in the liver suggested either a lower protei n degradation rate or a faster rate of threonine transport in the live r than in the pancreas. Threonine dehydrogenase activity was found onl y in the liver and the pancreas. Whereas Liver and pancreas threonine dehydrogenase specific activities were similar, glycine specific radio activity and enrichment were 12- to 14-fold higher in the pancreas tha n in the liver. This is probably the consequence of a higher productio n rate of glycine from sources other than threonine (protein degradati on, de novo synthesis from serine) in the liver than in the pancreas. Our results showed that Large White pigs could oxidize more threonine than Pietrain x Large White pigs. This could be related to the differe nce in growth performance and dietary N efficiency for protein deposit ion between these two genotypes.