Synthesis of citrulline and arginine from proline in enterocytes of postnatal pigs.
The synthesis of ornithine, citrulline, and arginine from proline was quantified in enterocytes of newborn (0-day-old) pigs, 2- to 21-day-old suckling pigs, and 29- to 58-day-old pigs weaned at 21 days of age. Mitochondria were prepared from enterocytes for measurement of proline oxidase activity. For metabolic studies, cells were incubated at 37 degrees C for 30 min in Krebs bicarbonate buffer (pH 7.4) containing 5 mM D-glucose and 0.0-5.0 mM L-[U-14C]proline with or without 2.0 mM L-glutamine. Proline oxidase activity and rates of synthesis of citrulline and arginine from proline were high in enterocytes of newborn pigs and markedly decreased in 7-day-old pigs. With increasing piglet age from 7 to 21 days, enterocyte proline oxidase activity and rate of conversion of proline into citrulline progressively increased, but the values in 21-day-old pigs remained much lower than in newborn pigs. The synthesis of ornithine, citrulline, and arginine from 0.5-5 mM proline was concentration dependent and required the addition of glutamine. About 80-90% of utilized proline carbons were recovered in ornithine plus citrulline plus arginine, with CO2 being a minor product. These results demonstrate a hitherto unrecognized pathway for the synthesis of ornithine, citrulline, and arginine via proline oxidase in enterocytes and challenge the current concept that pyrroline-5-carboxylate (P5C) is synthesized in the small intestine only from glutamine/glutamate via P5C synthase on the basis of previous work with postnatal rats.
Wu
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Department of Animal Science, Texas A&M University, College Station 77843, USA.
D000375:Aging / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D001120:Arginine / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002956:Citrulline / Q000378:metabolism*; D005260:Female; D007413:Intestinal Mucosa / Q000254:growth & development / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000201:enzymology; D008954:Models, Biological; D009952:Ornithine / Q000378:metabolism; D009953:Ornithine-Oxo-Acid Transaminase / Q000378:metabolism; D011392:Proline / Q000378:metabolism*; D011394:Proline Oxidase / Q000378:metabolism; D011865:Radioisotope Dilution Technique; D051381:Rats; D013552:Swine
D002250:Carbon Radioisotopes; D002956:Citrulline; D001120:Arginine; D011392:Proline; D009952:Ornithine; D011394:Proline Oxidase; D009953:Ornithine-Oxo-Acid Transaminase