Darcy B
Diabete Metab. 1984 May;10(2):121-33.
The supply of amino acids to the organism, required for maximum protein synthesis, results from several interdependent digestive processes: the sequential degradation of dietary proteins during their passage in the gastro-intestinal tract, and the absorption of their hydrolysis products. In this paper we survey the possible variations in these phenomena which are liable to affect amino acid availability. Concerns the transit of amino acids, we first examine gastric emptying which determines the length of stay of digestion products in the stomach and their passage to the small intestine. Thereafter the transit of digesta at the ileo-caeco-colic junction where the quantitative, qualitative and kinetic aspects of digestion in the small intestine may be investigated. The influence of the nature of proteins, and of their technological treatments is studied as well as the possible occurrence of a differential transit of free amino acids as compared to that of proteins and of proteins as compared to that of the carbohydrate fraction. With respect to enzyme hydrolysis, two kinds of problems may be considered: the accessibility of proteins to enzymes (due to the structure of proteins or of the other dietary components, or due to antinutritional factors), and the mode of action of some of the proteases (in particular trypsin, in relation with the involvement of technological treatments). The mechanisms thought to operate for normal absorption of free amino acids and oligopeptides are discussed, followed by some data concerning the absorption of amino acid derivatives, appearing during technological processing, and their influence on the absorption of normal forms of amino acids. The fate of the residual nitrogenous fraction in the large intestine, that is after the sites of amino acids release and absorption, is surveyed. A fundamental knowledge of these physiological processes may lead to development of methods estimating the yield of protein utilization in the digestive tract, based on the measurement either of amino acid disappearance from the lumen or of amino acid appearance in the portal blood. Digestion is a key step in the availability of amino acid, but it only gives a partial picture of this process. Therefore, its study should also be related to that of amino acid metabolism and overall protein synthesis.
为实现最大程度的蛋白质合成，机体所需的氨基酸供应源于多个相互依存的消化过程：膳食蛋白质在胃肠道中传递时的逐步降解，以及其水解产物的吸收。在本文中，我们探讨了这些现象中可能影响氨基酸可利用性的各种变化。关于氨基酸的转运，我们首先研究胃排空，它决定了消化产物在胃中的停留时间及其进入小肠的过程。此后，研究食糜在回盲结肠交界处的转运情况，在此可对小肠消化的定量、定性和动力学方面进行研究。我们还研究了蛋白质性质及其加工处理的影响，以及游离氨基酸与蛋白质、蛋白质与碳水化合物部分相比可能存在的差异转运情况。关于酶水解，可考虑两类问题：蛋白质对酶的可及性（由于蛋白质结构、其他膳食成分结构或抗营养因子所致），以及某些蛋白酶的作用方式（特别是胰蛋白酶，与加工处理的影响有关）。讨论了被认为是游离氨基酸和寡肽正常吸收所涉及的机制，随后介绍了一些关于技术加工过程中出现的氨基酸衍生物的吸收及其对正常形式氨基酸吸收影响的数据。考察了大肠中残留含氮部分的归宿，即氨基酸释放和吸收部位之后的情况。对这些生理过程的基本了解可能有助于开发基于测量肠腔中氨基酸消失或门静脉血中氨基酸出现情况来估算消化道蛋白质利用效率的方法。消化是氨基酸可利用性的关键步骤，但它只是该过程的部分情况。因此，对其研究还应与氨基酸代谢和整体蛋白质合成的研究相关联。
