Institute of Food Nutrition and Human Health, Massey University, Private Bag 121222, Palmerston North, New Zealand.
The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Batchelar Road, Palmerston North, 4474, New Zealand.
Rev Physiol Biochem Pharmacol. 2015;168:59-118. doi: 10.1007/112_2015_24.
Microvilli are conventionally regarded as an extension of the small intestinal absorptive surface, but they are also, as latterly discovered, a launching pad for brush border digestive enzymes. Recent work has demonstrated that motor elements of the microvillus cytoskeleton operate to displace the apical membrane toward the apex of the microvillus, where it vesiculates and is shed into the periapical space. Catalytically active brush border digestive enzymes remain incorporated within the membranes of these vesicles, which shifts the site of BB digestion from the surface of the enterocyte to the periapical space. This process enables nutrient hydrolysis to occur adjacent to the membrane in a pre-absorptive step. The characterization of BB digestive enzymes is influenced by the way in which these enzymes are anchored to the apical membranes of microvilli, their subsequent shedding in membrane vesicles, and their differing susceptibilities to cleavage from the component membranes. In addition, the presence of active intracellular components of these enzymes complicates their quantitative assay and the elucidation of their dynamics. This review summarizes the ontogeny and regulation of BB digestive enzymes and what is known of their kinetics and their action in the peripheral and axial regions of the small intestinal lumen.
微绒毛通常被认为是小肠吸收表面的延伸，但最近也发现，它也是刷状缘消化酶的起始点。最近的研究表明，微绒毛细胞骨架的运动元件作用是将顶膜推向微绒毛的顶端，在那里它形成囊泡并脱落到根尖间隙。催化活性的刷状缘消化酶仍然包含在这些囊泡的膜内，这将 BB 消化的部位从肠细胞表面转移到根尖间隙。这个过程使营养水解能够在吸收前的步骤中在膜附近发生。BB 消化酶的特性受到这些酶锚定在微绒毛顶膜的方式、随后在膜囊泡中的脱落以及它们对从组成膜中切割的不同敏感性的影响。此外，这些酶的活性细胞内成分的存在使它们的定量测定及其动力学及其在小肠腔的外周和轴向区域的作用变得复杂。这篇综述总结了 BB 消化酶的个体发生和调节，以及它们的动力学及其在小肠腔的外周和轴向区域的作用的已知情况。
