期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1987
卷号：84
期号：8
页码：2242-2245
DOI：10.1073/pnas.84.8.2242
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Because most eukaryotic somatic cells are bathed in a constant internal milieu, most of their proteins are constitutive, unlike the adaptive enzymes of bacteria. However, intestinal mucosal cells, like bacteria, face a varying milieu. Hence, we tested for adaptive regulation of intestinal nutrient transporters, sought its functional significance, and compared it with regulation of bacterial proteins. All 12 transporters studied proved to be regulated by dietary substrate levels. Regulation in the intestine is slower than in bacteria and shows lower peak-to-basal activity levels. Regulatory patterns vary greatly among transporters: two sugars and two nonessential amino acids monotonically up-regulate their transporters, two vitamins and three minerals monotonically down-regulate their transporters, and two transporters of essential amino acids respond nonmonotonically to levels of their substrates. These varied patterns arise from trade-offs among four factors: transporter costs, calories yielded by metabolizable substrates, fixed daily requirements of essential nutrients, and toxicity of certain nutrients in large amounts. Based on these trade-offs, we predict the form of regulatory pattern for intestinal transporters not yet studied.
