Schreurs V V, Boekholt H A, Koopmanschap R E, Weijs P J
Department of Human and Animal Physiology, Wageningen Agricultural University, The Netherlands.
Br J Nutr. 1992 Mar;67(2):207-14. doi: 10.1079/bjn19920024.
The present paper offers a dual 14CO2 breath test approach to study the metabolic utilization of free amino acids in the body. Using the carboxyl-[14C]isotopomer of an amino acid as the test substrate the percentage recovery of the isotope as 14CO2 reflects which part of the labelled amino acid flux has been decarboxylated. The residual C fragments may flow to total oxidation at least to the level recovered for the universal [14C]isotopomer. In the case that recovery for total oxidation is less than for decarboxylation, part of the [14C]fragments are retained in the body by either exchange or non-oxidative pathways. Utilization of tyrosine and leucine was measured in the post-absorptive phase in adult rats, conditioned on isoenergetic diets containing 210, 75 or 0 g protein/kg. It was shown that the level of dietary protein exerts an influence on both decarboxylation and total oxidation. Although the responses of leucine and tyrosine were not different for total oxidation, there was a difference between the amino acids in their relative rate of decarboxylation. That this dual 14CO2 breath test approach can be used as a tool to evaluate whether the protein and amino acid supply has been adequate to support actual requirements is discussed.
本文提供了一种双标记14CO2呼气试验方法，用于研究体内游离氨基酸的代谢利用情况。以氨基酸的羧基-[14C]同位素异构体作为测试底物，同位素以14CO2形式回收的百分比反映了标记氨基酸通量中发生脱羧反应的部分。剩余的C片段可能会至少以与通用[14C]同位素异构体回收水平相同的程度进行完全氧化。如果完全氧化的回收率低于脱羧反应的回收率，则部分[14C]片段会通过交换或非氧化途径保留在体内。在成年大鼠的吸收后阶段，以含210、75或0 g蛋白质/kg的等能量饮食为条件，测定了酪氨酸和亮氨酸的利用率。结果表明，饮食蛋白质水平对脱羧反应和完全氧化均有影响。尽管亮氨酸和酪氨酸在完全氧化方面的反应没有差异，但这两种氨基酸在脱羧反应的相对速率上存在差异。本文还讨论了这种双标记14CO2呼气试验方法能否作为一种工具，用于评估蛋白质和氨基酸供应是否足以满足实际需求。
