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Plasma and Urinary Methionine Levels in One-Year-Old Infants after Oral Loading with L-Methionine and N-Acetyl-L-Methionine¹

Departments of Pediatrics and Biochemistry, The University of Iowa College of Medicine, Iowa City, Iowa 52242

N-acetyl-L-methionine has been proposed as a replacement for methionine in supplementing food products low in this amino acid. Previous studies in adult subjects administered equimolar quantities (0.0605 mmoles/kg body weight) of L-methionine and N-acetyl-L-methionine showed equivalent overall release of methionine to the blood as judged by area under the plasma methionine time-absorption curve. In the present study, similar doses (0.0605 mmoles/kg body weight) of L-methionine and N-acetyl-L-methionine were administered to fasting 1-year-old infants in a randomized crossover design. The two compounds produced an equivalent overall release of methionine to the blood as judged by plasma methionine concentrations and by the area under the plasma methionine concentration-time curves. No evidence was obtained that indicated release of N-acetyl-L-methionine to plasma or its excretion in urine after loading. However, peak plasma methionine concentrations, and the areas under the plasma methionine concentration-time curves for infants were approximately one-half the values observed in normal adults administered equimolar doses of each compound on a per kilogram body weight basis. The data suggest more rapid metabolism of methionine and N-acetyl-L-methionine by infants than adults.

KEY WORDS: • methionine • N-acetyl-L-methionine • infants

¹ Supported in part by a grant-in-aid from the Procter and Gamble Co., Cincinnati, Ohio.

Manuscript received 28 August 1981.