Zello G A, Pencharz P B, Ball R O
Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.
Am J Physiol. 1993 Apr;264(4 Pt 1):E677-85. doi: 10.1152/ajpendo.1993.264.4.E677.
Lysine requirement was determined in seven adult males by examining the effect of varying dietary lysine intake on phenylalanine flux and oxidation under dietary conditions of adequate energy and phenylalanine (14 mg.kg-1 x day-1) and excess tyrosine (40 mg.kg-1 x day-1). Phenylalanine flux was determined from primed, constant intravenous infusions of L-[1-13C]phenylalanine (1.2 mg.kg-1 x day-1) and L-[ring-2H5]phenylalanine (0.5 mg.kg-1 x day-1) and measurement of isotopic enrichments of phenylalanine in plasma. Phenylalanine flux was not affected by graded increases in dietary lysine intake or by the isotope infused. Mean phenylalanine conversion to tyrosine was low (3.4%) and not significantly affected by lysine intake. Phenylalanine oxidation, estimated from the rate of 13CO2 released in expired air during the infusion of L-[1-13C]phenylalanine, decreased linearly as lysine intake increased to a break point that was interpreted as the mean dietary lysine requirement (37 mg.kg-1 x day-1). At lysine intakes of > 37 mg.kg-1 x day-1 phenylalanine oxidation was low and constant. Plasma lysine concentrations supported this estimate of requirement. These data show that: 1) indicator amino acid oxidation can be used as a new method to determine amino acid requirements of humans and 2) the lysine requirement of adult males is three times greater than the World Health Organization recommendation of 12 mg.kg-1 x day-1.
通过在充足能量和苯丙氨酸（14毫克·千克⁻¹·天⁻¹）以及过量酪氨酸（40毫克·千克⁻¹·天⁻¹）的饮食条件下，研究不同饮食赖氨酸摄入量对苯丙氨酸通量和氧化的影响，确定了7名成年男性的赖氨酸需求量。苯丙氨酸通量通过对L-[1-¹³C]苯丙氨酸（1.2毫克·千克⁻¹·天⁻¹）和L-[环-²H₅]苯丙氨酸（0.5毫克·千克⁻¹·天⁻¹）进行预充、持续静脉输注，并测量血浆中苯丙氨酸的同位素富集度来确定。苯丙氨酸通量不受饮食赖氨酸摄入量的分级增加或所输注同位素的影响。苯丙氨酸向酪氨酸的平均转化率较低（3.4%），且不受赖氨酸摄入量的显著影响。在输注L-[1-¹³C]苯丙氨酸期间，根据呼出气体中¹³CO₂的释放速率估算的苯丙氨酸氧化，随着赖氨酸摄入量增加至一个转折点而呈线性下降，该转折点被解释为平均饮食赖氨酸需求量（37毫克·千克⁻¹·天⁻¹）。当赖氨酸摄入量>37毫克·千克⁻¹·天⁻¹时，苯丙氨酸氧化较低且恒定。血浆赖氨酸浓度支持了这一需求量估计。这些数据表明：1）指示性氨基酸氧化可作为一种确定人类氨基酸需求量的新方法；2）成年男性的赖氨酸需求量是世界卫生组织推荐量12毫克·千克⁻¹·天⁻¹ 的三倍。
