title: Application of the indicator amino acid oxidation technique for the determination of metabolic availability of sulfur amino acids from casein versus soy protein isolate in adult men.
abstract: Our objective was to determine the metabolic availability (MA) of sulfur amino acids in dietary proteins using the indicator amino acid oxidation (IAAO) technique. Five to seven men received graded levels (20, 40, 60, and 70%) of the mean total sulfur amino acid (TSAA) requirement of 13 mg x kg(-1) x d(-1) as a crystalline AA mixture, casein, and soy protein isolate (SPI) (40, 50, 60, and 70%), respectively. Five of these subjects received 40% of TSAA requirement from SPI supplemented with methionine to the level of 40% of requirement. These 5 subjects also repeated the level of 60% TSAA requirements from both casein and SPI to assess repeatability. The mean MA of TSAA from SPI (71.8 +/- 3.6%) was lower than from casein (87.4 +/- 3.8%, P < 0.05). Supplementation of SPI with methionine decreased the IAAO (11.5 +/- 0.3% administered dose) compared with unsupplemented SPI (12.8 +/- 0.5% administered dose, P < 0.05). IAAO was similar for repeated measurements of casein and SPI, respectively, at the 60% TSAA intake level (10.8 +/- 1.0 vs. 10.7 +/- 1.2% for casein; 12.7 +/- 1.3 vs. 12.9 +/- 2.6% for SPI). In conclusion, the IAAO technique can be used to determine the MA of AA for protein synthesis in test proteins for humans.
authors.affiliation: Research Institute, Hospital for Sick Children, Toronto, ON, Canada M5G 1X8.
authors.forename: Mohammad A
authors.initials: MA
authors.lastname: Humayun
authors.forename: Rajavel
authors.initials: R
authors.lastname: Elango
authors.forename: Soenke
authors.initials: S
authors.lastname: Moehn
authors.forename: Ronald O
authors.initials: RO
authors.lastname: Ball
authors.forename: Paul B
authors.initials: PB
authors.lastname: Pencharz
mesh_terms: D000328:Adult; D000375:Aging / Q000378:metabolism*; D000603:Amino Acids, Sulfur / Q000378:metabolism* / Q000493:pharmacokinetics; D001682:Biological Availability; D001944:Breath Tests; D002364:Caseins / Q000378:metabolism* / Q000493:pharmacokinetics; D004044:Dietary Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008297:Male; D009751:Nutritional Requirements; D010084:Oxidation-Reduction; D030262:Soybean Proteins / Q000378:metabolism* / Q000493:pharmacokinetics
chemical_list: D000603:Amino Acids, Sulfur; D002364:Caseins; D004044:Dietary Proteins; D030262:Soybean Proteins