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PubMed1996

Why don't ruminal bacteria digest cellulose faster?

The bacteria Fibrobacter succinogenes, Ruminococcus flavefaciens, and Ruminococcus albus generally are regarded as the predominant cellulolytic microbes in the rumen. Comparison of available data from the literature reveals that these bacteria are the most actively cellulolytic of all mesophilic organisms described to date from any habitat. In light of numerous proposals to improve microbial cellulose digestion in ruminants, it is instructive to examine the characteristics of these species that contribute to their superior cellulolytic capabilities and to identify the factors that prevent them from digesting cellulose even more rapidly. As a group, these species have extreme nutritional specialization. They are able to utilize cellulose (or in some cases xylan) and its hydrolytic products as their nearly sole energy sources for growth. Moreover, each species apparently has evolved to similar maximum rates of cellulose digestion (first-order rate constants of 0.05 to 0.08 h-1). Active cellulose digestion involves adherence of cells to the fibers via a glycoprotein glycocalyx, which protects cells from protozoal grazing and cellulolytic enzymes from degradation by ruminal proteases while it retains-at least temporarily-the cellodextrin products for use by the cellulolytic bacteria. These properties result in different ecological roles for the adherent and nonadherent populations of each species, but overall provide an enormous selective advantage to these cellulolytic bacteria in the ruminal environment. However, major constraints to cellulose digestion are caused by cell-wall structure of the plant (matrix interactions among wall biopolymers and low substrate surface area) and by limited penetration of the nonmotile cellulolytic microbes into the cell lumen. Because of these constraints and the highly adapted nature of cellulose digestion by the predominant cellulolytic bacteria in the rumen, transfer of cellulolytic capabilities to noncellulolytic ruminal bacteria (e.g., by genetic engineering) that display other desirable properties offers limited opportunities to improve ruminal digestion of cellulose.

Animals↗
PubMed2006

Co-localization hypothesis: a mechanism for the intrapancreatic activation of digestive enzymes during the early phases of acute pancreatitis.

Acute pancreatitis is generally believed to be a disease in which the pancreas is injured by digestive enzymes that it normally produces. Most of the potentially harmful digestive enzymes produced by pancreatic acinar cells are synthesized and secreted as inactive zymogens which are normally activated only upon entry into the duodenum but, during the early stages of acute pancreatitis, those zymogens become prematurely activated within the pancreas and, presumably, that activation occurs within pancreatic acinar cells. The mechanisms responsible for intracellular activation of digestive enzyme zymogens have not been elucidated with certainty but, according to one widely recognized theory (the "co-localization hypothesis"), digestive enzyme zymogens are activated by lysosomal hydrolases when the two types of enzymes become co-localized within the same intracellular compartment. This review focuses on the evidence supporting the validity of the co-localization hypothesis as an explanation for digestive enzyme activation during the early stages of pancreatitis. The findings, summarized in this review, support the conclusion that co-localization of lysosomal hydrolases with digestive enzyme zymogens plays a critical role in permitting the intracellular activation of digestive enzymes that leads to acinar cell injury and pancreatitis.

Acute Disease↗
PubMed2000

A monoclonal antibody specific to the granulocyte-derived elastase-fragment D species of human fibrinogen and fibrin: its application to the measurement of granulocyte-derived elastase digests in plasma.

When granulocytes are stimulated under certain clinical conditions, elastase is released therefrom and digests fibrin(ogen) independently of the plasmin system, which may also be mobilized simultaneously. Thus, discrimination of these 2 systems becomes urgent for the diagnosis and treatment of the underlying diseases. Using as immunogen a 97-kd granulocyte-elastase digest of human fibrinogen, we raised an antibody IF-123 that specifically recognizes elastase digests of human fibrin(ogen). The 97-kd elastase fragment resembles plasmic fragment D(1), and the epitope of this antibody is located on the Aalpha (196-204) residue segment. This segment appears to be masked in fibrin(ogen) but exposed when the Aalpha Leu 204-Ile 205 peptide bond is cleaved by elastase. Cathepsin G concomitantly released from granulocytes failed to expose the epitope. By an enzyme immunoassay using IF-123 as the capture antibody, the elastase digests of fibrin(ogen) can be measured in plasma samples without interference by abundantly coexisting fibrinogen. Indeed, we found that the elastase digests were mostly elevated in patients with inflammation or malignant tumors, but remained in a normal range in patients with a benign gastrointestinal tract disease such as duodenal ulcer and polyps in the gallbladder or the colon. Like the plasmic D-dimer, the elastase digests predominantly consisted of the DD/E complex and DD/E-containing high-molecular weight derivatives apparently corresponding to the phase-3 plasmic digests of cross-linked fibrin. (Blood. 2000;95:1721-1728)

Amino Acid Sequence↗
PubMed2002

Co-digestion of energy crops and industrial confectionery by-products with cow manure: batch-scale and farm-scale evaluation.

The possible co-digestion of energy crops and industrial confectionery by-products with cow manure was evaluated firstly, through long-term batch experiments and secondly, in a farm-scale digester. In batch assays, digestion with mesophilically digested cow manure as inoculum resulted in specific methane yields (m3 kg(-1) VS added waste) of 0.35 for grass hay (particle size <1.0 cm); 0.26 for oats (0.5 cm) and 0.21 for clover (2.0 cm) harvested at vegetative stage and 0.14 (2.0 cm) for clover harvested at flowering stage. Specific methane yields (m3 kg(-1) VS added waste) for confectionery by-products were 0.37 for chocolate, 0.39 for black candy and 0.32 for confectionery raw material. Out the three particle sizes (2.0, 1.0 and 0.5 cm) tested, particle size of 1.0 cm was found ideal for digestion of grass hay and clover while, particle size reduction did not influence methane production from oats. Stage of the crop influenced the methane yields, with clover harvested at vegetative stage yielding 33% higher methane than when harvested at flowering stage. An approximate 60% enhancement in methane yield was noticed with the co-digestion of industrial confectionery wastes with cow manure in a full-scale farm digester.

Animal Feed↗
PubMed2005

Solving fecal coliform growth/reactivation in biosolids during full-scale post-digestion processes.

Fecal coliform recurrence has been observed at the City of Los Angeles Hyperion Treatment Plant during pilot-scale experiments with a designated thermophilic battery of six anaerobic digesters, while other digesters were still at a mesophilic temperature. Several lab and full-scale experiments indicated the following possible causes of the growth/reactivation of fecal coliforms in post-digestion: a) contamination of thermophilically digested biosolids with mesophilically digested biosolids; b) a large drop in the biosolids temperature between the centrifuges and silos, which could have allowed the reactivation and/or growth of fecal coliforms. These were resolved by the full plant conversion to thermophilic anaerobic digestion and design modifications of the post-digestion train.

Bacteria, Anaerobic↗
PubMed1991

Characterization of a limited trypsin digestion form of eukaryotic elongation factor 1 alpha.

The involvement of the first 69 amino acids of eukaryotic elongation factor 1 alpha (EF-1 alpha) from rabbit reticulocyte in GTP and aminoacyl-tRNA binding has been analyzed by a variety of techniques. EF-1 alpha was subjected to limited trypsin digestion, which cleaved predominantly at residues 36 and 69. A digested form of Escherichia coli EF-Tu, similar to the one used for this study, has been characterized by x-ray crystallography and is used as a structural model for EF-1 alpha. This form of EF-1 alpha bound E. coli Phe-tRNAPhe similar to the wild type protein, but lacked activity in phenylalanine polymerization with poly(U)-programmed ribosomes. These results were obtained regardless of whether or not loosely associated N-terminal peptides were removed by gel filtration chromatography. The digested EF-1 alpha also shows reduced GTPase activity, but the activity is stimulated by both ribosomes and aminoacyl-tRNA. Binding of EF-1 alpha to the 80 S ribosome, as determined by association of reductively methylated protein through Sepharose 6B chromatography, is reduced approximately 7-fold for the limited digested form of the protein. Limited digested EF-1 alpha can, however, be photo-cross-linked with GTP and 3'-p-azido-GTP similar to intact EF-1 alpha. Chemical cross-linking with oxidized GTP, fluorosulfonylbenzoyl-GTP, or with trans-diaminedichloroplatinum(II) and GPT, shows a similar modification of both intact and limited digested EF-1 alpha. In order to further localize the modification site with the GTP reagents and assure that modification was not occurring in the first 69 amino acids, intact EF-1 alpha was modified with these same reagents. Limited trypsin digestion of modified protein indicates that none of these reagents cross-links GTP to the first 69 amino acids of EF-1 alpha, which includes the first GTP binding consensus element, GXXXXGK.

Affinity Labels↗
PubMedDate not supplied

Evaluation of protein digestibility-corrected amino acid score method for assessing protein quality of foods.

The current concepts of protein quality evaluation were reviewed. A detailed examination of existing animal assays and more promising amino acid scoring methods has been carried out by an Ad Hoc Working Group on Protein Quality Measurement for the Codex Committee on Vegetable Proteins during the last 5 years. Several factors such as inadequacies of protein efficiency ratio (PER, the poorest test) and other animal assays, advancements made in standardizing methods for amino acid analysis and protein digestibility, availability of data on digestibility of protein and individual amino acids in a variety of foods, and reliability of human amino acid requirements and scoring patterns were evaluated. On the basis of this evaluation, amino acid score, corrected for true digestibility of protein, was recommended to be the most suitable routine method for predicting protein quality of foods for humans. Amino acid scores corrected for true digestibility of protein (as determined by rat balance method) were termed "protein digestibility-corrected amino acid scores." A detailed method for the determination of the protein digestibility-corrected amino acid score was proposed, and information about the range of scores to be expected in foods or food products was provided in the present investigation. The protein digestibility-corrected amino acid score method is a simple and scientifically sound approach for routine evaluation of protein quality of foods. Accuracy of the method would, however, be confirmed after validation with growth or metabolic balance studies in humans.

Amino Acids↗
PubMed1990

Cantharidin decreases in vitro digestion of alfalfa and smooth bromegrass.

Blister beetles (Coleoptera:Meloidae) containing the toxin cantharidin can be incorporated with alfalfa (Medicago sativa L) during forage conservation. Cantharidin inadvertently ingested with animal feed may cause illness or death. Little information is available on the effects of cantharidin on ruminant microbial digestion. The objective of our study was to determine cantharidin effects on digestibility of alfalfa and smooth bromegrass (Bromus inermis Leyss) by measuring in vitro digestible dry matter (IVDDM) and cell wall digestion (CWD). Alfalfa dry matter digestibility, measured after IVDDM at 48 and 96 h fermentation periods, decreased as cantharidin concentration increased. Increasing cantharidin concentration also significantly reduced IVDDM of smooth bromegrass at 24 and 96 h digestion time. The CWD of alfalfa and smooth bromegrass decreased as cantharidin concentration increased. These results indicate that ingestion of cantharidin by ruminants may decrease microbial digestion of fibrous feeds and therefore may decrease the efficiency of feed utilization by ruminants.

Animals↗
PubMed1984

[Protein digestibility and energy in diets based on rice and beans in human adults].

Four studies were carried out for the purpose of measuring the digestibility of diets based on rice and beans (Phaseolus vulgaris), and in order to quantify the effect of their supplementation with animal protein (milk) and energy (oil), on the energy and protein digestibility of such diets in human adults. Diets were offered so that they supplied 46, 72, and 103 mg N/kg/day. When the basal diet--where rice provided 60% of the protein and beans 40%--was administered at a level of 102.5 mg of nitrogen/kg/day and 49.5 Kcal/kg/day of gross energy, an apparent and true nitrogen, energy and metabolizable energy digestibility of 59.1, 70.8, 93.8 and 92.5%, respectively, were observed. When substituting 10% of the vegetable protein by milk protein in the same diet, the same indicators revealed a digestibility of 65.3, 76.8, 93.5 and 92.1%, respectively. The information indicates that supplementation with animal protein improves nitrogen absorption at any of the energy levels studied. In contrast, caloric supplementation does not have any positive effect on nitrogen or energy absorption. It was also found that nitrogen apparent digestibility increases significantly when the N level in the diet is raised, and stabilizes when intake exceeds 100 mg nitrogen/kg/day. It is therefore proposed that for digestibility studies in diets where animal protein is utilized at a nitrogen level of around 120 mg/kg/day, true digestibility remains constant, no matter what nitrogen level is used in the diet.

Adult↗
PubMed1986

The digestive strategy and efficiency of the West Indian manatee, Trichechus manatus.

During the winters of 1982/83 and 1983/84, samples of digesta were collected from nine sites along the gastrointestinal tracts of seven West Indian manatees, Trichechus manatus. The voluminous large intestine of the manatee is responsible for considerable water reabsorption, as well as being the major site of organic matter, nitrogen and crude fat digestion. Cellulose digestion occurs primarily in the cecum and anterior portion of the colon in a pattern similar to terrestrial nonruminant herbivores like the horse. Overall digestibility coefficients for organic matter (71%), nitrogen (61%) and crude fat (77%) are comparable to those of terrestrial herbivores. Manatees have one of the highest digestibility coefficients for cellulose (80%) of any known mammalian herbivore. This high efficiency of cellulose digestion is due primarily to an extremely slow rate of passage. In addition, it appears that seagrasses may be more digestible than terrestrial forages, possibly due to their relatively low lignin content.

Animals↗
PubMed2003

A physiological and biochemical model for digestion in the ectoparasitic mite, Psoroptes ovis (Acari: Psoroptidae).

Mites are an important group of arthropod pests affecting crops, animals and humans. Despite this, detailed physiological studies on these organisms remain sparse due largely to their small size. Unifying models are required to draw together the diverse information from studies on different groups and species. This paper describes a model for digestion in the parasitic mite, Psoroptes ovis, the causative agent of psoroptic mange or sheep scab disease. The limited information about this species is supplemented with data from other acarines, especially house dust mites and ticks. We review the range of enzymes and allergens found in mites and consider their possible roles in digestion in mites, generally and in particular, P. ovis. Histological studies, enzyme biochemistry and molecular biology and experimental evidence suggest that P. ovis utilises a digestive system reliant upon acid peptidases functioning in a largely intracellular environment. The actions of the digestive enzymes are supplemented by the involvement of bacteria as potential direct and indirect sources of nutrition. It is possible that some extra-corporeal digestion also takes place. The interaction of bacteria and digestive enzymes on the skin surface of the sheep may be responsible for the excessive pathological reactions evident in clinical sheep scab.

Animals↗
PubMed2002

Digestive proteinases of Brycon orbignyanus (Characidae, Teleostei): characteristics and effects of protein quality.

Juvenile piracanjuba, Brycon orbignyanus, in the wild consume protein from both plant and animal sources. Digestion of protein in piracanjuba begins in the stomach with pepsin, at low pH, and is followed by hydrolysis at alkaline pH in the lumen of the intestine. The digestive system in piracanjuba was evaluated to characterize the enzymes responsible for the digestion of feed protein and their composition. The gastric tissue synthesizes pepsin and the intestine tissues trypsin and chymotrypsin. Operational variables were evaluated and defined for future studies of the digestive system physiology. The enzymatic activity in the intestine and the relative concentration of enzymes were heavily influenced by the composition of the feed and the feeding regime, as detected by substrate-SDS-PAGE. Piracanjuba possess a mechanism of enzyme adaptation responding to food quality and regime, by varying the amount and composition of digestive proteases. This is a requisite study to determine the enzymes digesting protein in food and their characteristics and to gain some clues about the possible regulation mechanisms of enzyme synthesis in piracanjuba.

Adaptation, Physiological↗
PubMed2004

Angiotensin converting enzyme inhibitory activity in commercial fermented products. Formation of peptides under simulated gastrointestinal digestion.

The angiotensin converting enzyme (ACE)-inhibitory activity of several commercial fermented milks was evaluated. Most of these products showed moderate inhibitory activity, but a few exceptions were detected. The high ACE-inhibitory activity found in some cases could be related to the origin of the milk. Two of these products were subjected to an enzymatic hydrolysis process, which simulates physiological digestion, to study the influence of digestion on ACE-inhibitory activity. The activity did not significantly change or increase during simulated gastrointestinal digestion. The peptides generated from one selected product during simulated digestion were sequenced by tandem spectrometry. Most peptides found at the end of the simulated digestion were released after 30 min of incubation with the pancreatic extract. This suggests that physiological digestion promotes the formation of active peptides from the proteins present in these fermented products. The potential ACE-inhibitory activity of the identified peptides is discussed with regard to their amino acid sequences.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1981

Digestive enzymes in the germ-free animal.

The digestive physiology of the germ-free animal has a number of characteristics (cecal hypertrophy, slower small intestine cell renewal, slower gastric emptying and intestinal transit) which distinguish it from that of the conventional animal. If the germ-free model is to be used to determine the role of gastrointestinal microflora in the nutrition of the conventional animal, it is essential to complete the study of these characteristics by data on digestive enzymes in the germ-free. The present paper analyzes these data. There is little information on salivary amylase and none on gastric proteolytic enzymes and intestinal peptidases. More complete data on exocrine pancreas enzymes and intestinal disaccharidases show that the digestive equipment is similar in germ-free and conventional animals. Bile salts, not considered as digestive enzymes, are qualitatively and quantitatively different, depending on the digestive tract bacterial environment. In general, the germ-free animal has some characteristics which should permit better utilization of the diet ingested. Measurements of apparent digestibility do not confirm this hypothesis since results obtained in germ-free and conventional animals of the same species are contradictory.

Animals↗
PubMed2000

Biological clocks and the digestive system.

Circadian rhythms play a major role in regulating the digestive systems of many organisms. Cell proliferation, migration, differentiation, and even structure vary as a function of time of day in many different digestive organs (i.e., stomach, gut, liver, and pancreas) and cell types, resulting in regionally specific temporal variations in protein and gene expression. Feeding and light set the hands of the digestive clock(s). However, the clockwork has a genetic basis. During the last 10 years, new developments have emerged in our understanding of how cells keep time. Surprisingly, clock genes in mammals are expressed not only in specialized time keepers in the brain, but also in peripheral organs, suggesting that the ability to keep time may also belong to cells within the digestive system. This article reviews several classic examples of circadian variation in the digestive system, with an emphasis on rhythms in cell proliferation, function, and structure. It also briefly summarizes several new ideas about how cells in the brain and possibly the digestive system keep time.

Animals↗
PubMed1985

The effect of provision of the first-limiting amino acid, gastrointestinal microbial activity and the level of nitrogen intake on protein utilization and energy digestibility in rats.

1. The present work with growing rats was undertaken to study the effect of protein quality, gastrointestinal microbial activity and the level of nitrogen intake on protein utilization and energy digestibility. The experiment involved a total of thirty-six dietary treatments in a 9 x 4 factorial design, with five rats per treatment. The thirty-six diets resulted from nine protein sources. Each diet was composed of a basal N-free mixture plus minerals and vitamins, with N sources added at the expense of the N-free mixture to provide 15.0 gN/kg dry matter (DM) in the first three protein-addition treatments and 30.0 gN/kg DM in the fourth protein-addition treatment. The nine protein sources were soya-bean meal, casein, wheat gluten, skim-milk powder, meat-and-bone meal, wheat bran, barley, wheat and cooked brown beans (Phaseolus vulgaris). The four formulations for each protein source incorporated the protein unsupplemented at 15.0 gN/kg DM, unsupplemented at 30.0 gN/kg DM, or supplemented at 15.0 gN/kg DM with the estimated first-limiting amino acid or the antibiotic Nebacitin. 2. With all protein sources, the inclusion of the first-limiting amino acid had no effect on either protein or energy digestibility. 3. The microbial activity in the digestive tract affected protein utilization and energy digestibility to a different degree depending primarily on the level and type of dietary fibre. True protein digestibility (TD) of skim-milk powder and brown beans, both rich in easily-fermentable energy, increased from 0.959 to 1.000 and from 0.680 to 0.777 respectively by the addition of Nebacitin. TD of the other protein sources was only marginally affected by the antibiotic treatment. Only with brown beans was the biological value (BV) markedly affected by Nebacitin with an increase from 0.482 to 0.557 by the treatment. Energy digestibility was significantly lower in rats given antibiotic with soya-bean meal, wheat bran, barley, wheat and brown beans. 4. The effect of level of N intake on protein utilization was dependent on both protein quality and the fibre concentration of the diet. Protein sources with high BV were more affected than proteins of lower BV. It was concluded that TD is not always independent of dietary protein concentration.

Amino Acids↗
PubMed1996

The influence of dietary fibre source and level on the development of the gastrointestinal tract, digestibility and energy metabolism in broiler chickens.

The present study was undertaken to provide detailed information about the effect of fibre source (pea fibre, wheat bran or oat bran) at inclusion levels of 0, 187 and 375 g/kg diet on the development of the digestive tract, nutrient digestibility and energy and protein metabolism in broiler chickens. Heat production was measured using open-air-circuit respiration chambers. Diets with increasing levels of pea fibre decreased the DM in droppings and increased excreta output (2.5-fold) relative to DM intake. Adaptation to increased dietary fibre levels included increases in the size of the digestive system, with pea fibre exerting a stronger impact than wheat bran or oat bran. The length of the intestine, and particularly the length and weight of the caecum, increased with the fibre level. The digestibility of all nutrients also decreased with increasing fibre level. The decrease in the digestibility in relation to NSP for the three fibre sources was bigger for oat bran (0.0020 per g dietary NSP) than for pea fibre and wheat bran (0.0014 and 0.0016 per g dietary NSP) indicating that the cell walls in oat bran (aleurone and subaleurone) had a significant negative effect on the digestibility of cellular nutrients, i.e. protein and fat. The degradation of the NSP constituents was far lower in chickens than found in other animal species such as pigs and rats, thus supporting the view that chickens do not ferment fibre polymers to a great extent. Excretion of organic acids (mainly lactic acid and acetic acid) accounted for up to 2% of metabolizable energy (ME) intake with the highest excretion for the high-fibre diets. H2 excretion was related to the amount of NSP degraded and indicated higher microbial fermentation with increasing fibre levels. The chickens' feed intake responded to a great extent to dietary ME concentration but expressed in terms of metabolic body size (W0.75) ME intake was depressed at the high fibre levels. Dietary NSP was able to explain between 86% (oat bran) and 96% (pea fibre) of the variation in ME concentration. The amount of energy available from fermentation of NSP appears to reach a maximum of 42 kJ/d independent of fibre source and level. Expressed in relation to ME intake the NSP fermentation contributed 3-4%. With increasing fibre intake the partitioning of retained energy between body protein and body fat changed in favour of protein.

Animals↗
PubMedDate not supplied

Digestive response to restricted feeding in migratory yellow-rumped warblers.

Smaller guts and slow initial mass gains at stopover sites have led to the idea that digestive physiology limits refueling rates in migrating birds. We tested the digestive-limitation hypothesis in yellow-rumped warblers using food restriction to simulate infrequent feeding during migration, which may cause a reduction in alimentary tract mass. Restricted birds had small intestine, pancreas, and liver masses 18%-22% lower than ad lib.-fed controls. Total activities of sucrase, maltase, aminopeptidase, and amylase were significantly lower in restricted birds, while those of trypsin and chymotrypsin were not. Only aminopeptidase mass-specific activity was significantly lower in restricted birds. Previously restricted birds were able to feed and digest at a high rate immediately following return to ad lib. feeding. Digestive efficiency did not differ between groups. These results suggest that before migration yellow-rumped warblers have some spare digestive capacity to compensate for declines in their digestive organ masses during migration.

Adaptation, Physiological↗