Expression and intracellular transport of microvillus membrane hydrolases in human intestinal epithelial cells

A panel of monoclonal antibodies was produced against purified microvillus membranes of human small intestinal enterocytes. By means of these probes three disaccharidases (sucrase-isomaltase, lactase-phlorizin hydrolase, and maltase-glucoamylase) and four peptidases (aminopeptidase N, dipeptidylpeptidase IV, angiotension I-converting enzyme, and p-aminobenzoic acid peptide hydrolase) were successfully identified as individual entities by SDS PAGE and localized in the microvillus border of the enterocytes by immunofluorescence microscopy. The antibodies were used to study the expression of small intestinal hydrolases in the colonic adenocarcinoma cell line Caco 2. This cell line was found to express sucrase-isomaltase, lactase-phlorizin hydrolase, aminopeptidase N, and dipeptidylpeptidase IV, but not the other three enzymes. Pulse-chase studies with [35S]methionine and analysis by subunit-specific monoclonal antibodies revealed that sucrase-isomaltase was synthesized and persisted as a single-chain protein comprising both subunits. Similarly, lactase-phlorizin hydrolase was synthesized as a large precursor about twice the size of the lactase subunits found in the human intestine. Aminopeptidase N and dipeptidylpeptidase IV, known to be dimeric enzymes in most mammals, were synthesized as monomers. Transport from the rough endoplasmic reticulum to the trans-Golgi apparatus was considerably faster for the peptidases than for the disaccharidases, as probed by endoglycosidase H sensitivity. These results suggest that the major disaccharidases share a common biosynthetic mechanism that differs from that for peptidases. Furthermore, the data indicate that the transport of microvillus membrane proteins to and through the Golgi apparatus is a selective process that may be mediated by transport receptors.     

Factors regulating tropane-alkaloid production in a transformed root culture of a Datura candida × D. aurea hybrid

Using in combination an analysis of (i) the levels of enzyme activities present, (ii) the pool sizes of metabolic intermediates and end products and (iii) the effects of feeding metabolic intermediates, the limitations ? flux into tropane alkaloids in a Datura root culture have been examined. This culture, produced by transforming a Datura candida × D. aurea hybrid with Agrobacterium rhizogenes, is found to be highly competent in the biosynthesis of both hyoscyamine and scopolamine as well as a wide range of other hygrine-derived alkaloids. It has been found that, of six enzymes which are involved in this pathway, the two initial activities, ornithine decarboxylase (EC 4.1.1.17) and arginine decarboxylase (EC 4.1.1.19), are present at potentially flux-limiting levels, in contrast to those other enzymes assayed which act further down the pathway. An additional limitation to flux, involving the supply of activated acids for condensation with tropine to form the identified tropoyl and tigloyl derivatives, is also indicated from the observed effect of feeding free acids. The relative contribution to flux limitation caused by these two interacting phenomena is inferred from an analysis of the changing relative levels of metabolic intermediates and end products as cultures mature.     

Ontogeny of a novel pituitary protein (7B2) in the human fetal intestine

The developmental profile of the concentration of a novel pituitary protein (7B2) was studied immunochemically in the human gastrointestinal tract from 12 weeks of gestation to 4 months after birth and was compared to the distribution in the adult. 7B2-like immunoreactivity (IR-7B2) was detected in all segments studied, but no gross changes were seen through fetal life. At term higher concentrations of IR-7B2 were found in the duodenum and the antrum, which is similar to the distribution of adult man. Gel permeation chromatography revealed that the main peak of 7B2 immunoreactivity in the fetal intestinal extract eluted with a Kav of 0.3. Similar elution profiles were also observed in extracts of human adult intestine.     

Molecular details of tomato extensin and glycine-rich protein gene expression

In a recent publication (Plant Molecular Biology 16: 547–565 (1991)) Showalter et al. described the isolation and initial characterization of fifteen extensin and extensin-like tomato cDNAs. These cDNAs were determined to fall into five distinct classes; class I and II clones encoded extensins, class III and V clones encoded glycine-rich proteins (GRPs), and class IV clones encoded a portion of a GRP sequence on one DNA strand and a portion of an extensin sequence on the other DNA strand. In this publication, a more detailed analysis of the expression of these cDNA classes was performed with respect to wounding in various tomato organs, development, kinetics and systemic extent of the wound response, ethylene treatment, abscisic acid (ABA) treatment, and drought stress by using RNA gel blot hybridizations. In general, extensin gene expression was readily detected in stems and roots, but not in leaves. With both class I and II extensin cDNA probes, wound-induced accumulation of mRNA in stems was first detected between 4 and 8 h after wounding with maximal accumulation occurring after 12 h. Moreover, these extensin wound responses were detected locally at the wound site but not systemically. Expression of the class III GRP was largely limited to wounded stem tissue. Initial detection and maximal accumulation of the class III GRP mRNA was similar to the extensins mRNAs; however, this GRP wound response occurred both locally and systemically. Additionally, abscisic acid treatment and drought stress resulted in the marked accumulation of the class III GRP mRNA in tomato stems, but did not alter the expression of the other cDNA classes. In contrast, expression of the class V GRP occurred in stems and roots and to a lesser extent in leaves and decreased in response to wounding over a 24 h time period. The class V GRP wound response was further characterized by an early, transient accumulation of mRNA occurring 2–4 h after wounding in stems and by its local nature.     

Somatostatin and the dumping syndrome.

Infusion of somatostatin reduced the symptoms of the early dumping syndrome after oral glucose was given and also reduced the associated tachycardia and rise in packed cell volume. It inhibited the secretion of enteroglucagon, neurotensin, and vasoactive intestinal polypeptide, which are raised in patients with the dumping syndrome and may have an aetiological role. It also prevented the reactive hypoglycaemia of late dumping by inhibiting the release of gastric inhibitory polypeptide and insulin. Somatostatin, possibly through its inhibitory effects on hormonal secretion, may have a role in the management of patients with the early and late dumping syndrome.     

Defining a land boundary for sustainable livestock consumption

The need for more sustainable production and consumption of animal source food (ASF) is central to the achievement of the sustainable development goals: within this context, wise use of land is a core challenge and concern. A key question in feeding the future world is: how much ASF should we eat? We demonstrate that livestock raised under the circular economy concept could provide a significant, nonnegligible part (9–23 g/per capita) of our daily protein needs (~50–60 g/per capita). This livestock then would not consume human‐edible biomass, such as grains, but mainly convert leftovers from arable land and grass resources into valuable food, implying that production of livestock feed is largely decoupled from arable land. The availability of these biomass streams for livestock then determines the boundaries for livestock production and consumption. Under this concept, the competition for land for feed or food would be minimized and compared to no ASF, including some ASF in the human diet could free up about one quarter of global arable land. Our results also demonstrate that restricted growth in consumption of ASF in Africa and Asia would be feasible under these boundary conditions, while reductions in the rest of the world would be necessary to meet land use sustainability criteria. Managing this expansion and contraction of future consumption of ASF is essential for achieving sustainable nutrition security.