TY - JOUR
T1 - VLDL apolipoprotein B-100, a potential indicator of the isotopic labeling of the hepatic protein synthetic precursor pool in humans
T2 - Studies with multiple stable isotopically labeled amino acids
AU - Reeds, P. J.
AU - Hachey, D. L.
AU - Patterson, B. W.
AU - Motil, K. J.
AU - Klein, P. D.
PY - 1992
Y1 - 1992
N2 - Four adult men received a 48-h constant intravenous infusion of [2H4]lysine, [2H3]leucine, L-[ring-13C6]phenylalanine, and L-[1,2,3,- 13C3]alanine. Subjects ingested hourly meals for two 12-h periods, separated by two 12-h fasting periods. The isotopic enrichments of free amino acids in venous plasma and in VLDL apolipoprotein B-100 (apoB)-bound amino acids, plasma α-keto isocaproic acid (α-KIC) and plasma pyruvic acid (PYR) were measured by negative chemical ionization gas chromatography-mass spectrometry. By 7 h of infusion, all four amino acids achieved an equilibrium isotopic enrichment (EIE) in plasma and in apoB. In the fed state, the EIE of the amino acids in apoB was lower than that in plasma free amino acids. The ratio EIE-apoB:EIE-plasma differed significantly among amino acids in the fed state (alanine 0.30; lysine 0.64; leucine 0.70; phenylalanine 0.81). In the postabsorptive state, the EIE-apoB:EIE-plasma ratio rose significantly compared with the fed state (alanine 0.38; lysine 0.73; leucine 0.94; phenylalanine 1.05). Plasma PYR and apoB-alanine were in isotopic equilibrium irrespective of nutritional state. The EIE-apoB- leucine:EIE-plasma-α-KIC ratio rose from 0.75 in the fed state to near 1 in the postabsorptive state. We conclude that the contribution of systemic amino acids to apoB-100 synthesis is sensitive to nutritional state, and that systemic essential amino acids seem to be preferentially incorporated into apoB.
AB - Four adult men received a 48-h constant intravenous infusion of [2H4]lysine, [2H3]leucine, L-[ring-13C6]phenylalanine, and L-[1,2,3,- 13C3]alanine. Subjects ingested hourly meals for two 12-h periods, separated by two 12-h fasting periods. The isotopic enrichments of free amino acids in venous plasma and in VLDL apolipoprotein B-100 (apoB)-bound amino acids, plasma α-keto isocaproic acid (α-KIC) and plasma pyruvic acid (PYR) were measured by negative chemical ionization gas chromatography-mass spectrometry. By 7 h of infusion, all four amino acids achieved an equilibrium isotopic enrichment (EIE) in plasma and in apoB. In the fed state, the EIE of the amino acids in apoB was lower than that in plasma free amino acids. The ratio EIE-apoB:EIE-plasma differed significantly among amino acids in the fed state (alanine 0.30; lysine 0.64; leucine 0.70; phenylalanine 0.81). In the postabsorptive state, the EIE-apoB:EIE-plasma ratio rose significantly compared with the fed state (alanine 0.38; lysine 0.73; leucine 0.94; phenylalanine 1.05). Plasma PYR and apoB-alanine were in isotopic equilibrium irrespective of nutritional state. The EIE-apoB- leucine:EIE-plasma-α-KIC ratio rose from 0.75 in the fed state to near 1 in the postabsorptive state. We conclude that the contribution of systemic amino acids to apoB-100 synthesis is sensitive to nutritional state, and that systemic essential amino acids seem to be preferentially incorporated into apoB.
KW - humans
KW - lipoprotein
KW - liver
KW - protein synthesis
UR - http://www.scopus.com/inward/record.url?scp=0026558054&partnerID=8YFLogxK
U2 - 10.1093/jn/122.3.457
DO - 10.1093/jn/122.3.457
M3 - Article
C2 - 1542004
AN - SCOPUS:0026558054
SN - 0022-3166
VL - 122
SP - 457
EP - 466
JO - Journal of Nutrition
JF - Journal of Nutrition
IS - 3
ER -