Ancylostoma ceylanicum and Nippostrongylus brasiliensis decarboxylated most of the amino acids examined, but only a few at signficant rates. The former nematode in general possessed higher activites. Striking differences between the two parasites were, however, noticed regarding the metabolism of some of the amino acids. For instance, while alanine followed by asparate produced highest amounts of 14CO2in the presence of A. ceylanicum, proline exhibited maximum decarboxlation in case of N. brasiliensis. Tyrosine, on the other hand, did not libreate detectable CO2with either parasite. Likewise, although large number of amino acids underwent transmination with 2-oxoglutarate, only some of them elicited appreciable activity for any two parasites.

The present study investigated the relative importance of glutamine as a transamination source in the ovine liver by examination of the labelling of amino acids (AA) in the hepatic free pool, mixed liver and plasma proteins of fed and fasted sheep, following infusion of isotopically-labelled glutamine. In a cross-over design four sheep were either fasted for 3 d or fed to 1·2×energy maintenance and finally euthanased. At each intake, the sheep were infused for 6 h with [2-15N]glutamine (150 μmol/h) and samples of total plasma protein isolated. Following the terminal infusion, liver tissue total proteins were prepared and hydrolysed and 15N-enrichments in seventeen AA were determined by GC–combustion–isotope-ratio mass spectrometry. All AA were enriched (relative to natural abundance) except lysine and threonine, with the lowest enrichments in phenylalanine and histidine. There was no effect of the fed v. fasted state, except for leucine and isoleucine in liver protein (P<0·05). Enrichments in liver protein were greater than in plasma protein (P<0·01, except proline) and probably reflect the faster turnover rate of hepatic constitutive proteins compared with export proteins. Amination to methionine was greater than that to phenylalanine (P<0·01), suggesting a mechanism for preferentially protecting the former. This factor could be important for ruminant production, as methionine is often considered to be the first limiting AA for animals offered certain silages and conserved forages. Enrichments in all AA (except for glutamine, alanine and aspartate) were less than that for glutamate (P<0·01), and thus transaminations may have occurred with glutamine directly or via glutamate, following the action of hepatic glutaminase.