Synthesis of citrulline from glutamine in pig enterocytes.
The synthesis of citrulline from glutamine was quantified in enterocytes from pre-weaning (14-21 days old) and post-weaning (29-58 days old) pigs. The cells were incubated at 37 degrees C for 30 min in Krebs-Henseleit bicarbonate buffer (pH 7.4) containing 0, 0.5, 2 and 5 mM glutamine. Oxygen consumption was linear during the 30 min incubation period. The rates of citrulline synthesis were low or negligible in enterocytes from 14-21-day-old pigs, but increased 10-20-fold in the cells from 29-58-day-old pigs. This marked elevation of citrulline synthesis coincided with an increase in the activity of pyrroline-5-carboxylate synthase with the animal's post-weaning growth. In contrast, decreases in the activities of phosphate-dependent glutaminase, ornithine aminotransferase, ornithine carbamoyltransferase and carbamoyl-phosphate synthase were observed as the age of the pigs increased. The concentrations of carbamoyl phosphate in enterocytes from pre-weaning pigs were higher than, or similar to, those in the cells from post-weaning pigs. It is possible that the low rate of citrulline synthesis from glutamine in enterocytes from pre-weaning pigs was due to a limited availability of ornithine, rather than that of carbamoyl phosphate. We suggest that this limited availability of ornithine in pre-weaning-pig enterocytes results from (i) the low rate of pyrroline-5-carboxylate synthesis from glutamate, due to the low activity of pyrroline-5-carboxylate synthase, and (ii) the competitive conversion of pyrroline-5-carboxylate into proline. Our present findings on the developmental aspect of citrulline synthesis in pig enterocytes may offer a biochemical mechanism for the previous observations that arginine is a nutritionally essential amino acid for suckling piglets, but not for adult pigs.
Wu
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G
Department of Animal Science, Texas A&M University, College Station 77843-2471.
Knabe
D A
DA
Flynn
N E
NE
D000641:Ammonia / Q000494:pharmacology; D000818:Animals; D019731:Carbon-Nitrogen Ligases; D002956:Citrulline / Q000096:biosynthesis*; D005260:Female; D005972:Glutaminase / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism*; D007583:Jejunum / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D008025:Ligases / Q000378:metabolism; D008297:Male; D009952:Ornithine / Q000494:pharmacology; D009954:Ornithine Carbamoyltransferase / Q000378:metabolism; D009953:Ornithine-Oxo-Acid Transaminase / Q000378:metabolism; D011392:Proline / Q000494:pharmacology; D013552:Swine
D005973:Glutamine; D002956:Citrulline; D000641:Ammonia; D011392:Proline; D009952:Ornithine; D009954:Ornithine Carbamoyltransferase; D009953:Ornithine-Oxo-Acid Transaminase; D005972:Glutaminase; D008025:Ligases; D019731:Carbon-Nitrogen Ligases; C024233:carbamoyl-phosphate synthetase (N-acetylglutamate)