Showing papers on "Urea published in 1979"

Counteraction of urea destabilization of protein structure by methylamine osmoregulatory compounds of elasmobranch fishes.

Abstract: Intracellular fluids of marine elasmobranchs (sharks, skates and rays), holocephalans and the coelacanth contain urea at concentrations averaging 0.4m, high enough to significantly affect the structural and functional properties of many proteins. Also present in the cells of these fishes are a family of methylamine compounds, largely trimethylamine N-oxide with some betaine and sarcosine, and certain free amino acids, mainly β-alanine and taurine, whose total concentration is approx. 0.2m. These methylamine compounds and amino acids have been found to be effective stabilizers of protein structure, and, at a 1:2 molar concentration ratio of these compounds to urea, perturbations of protein structure by urea are largely or fully offset. These counteracting effects of solutes on proteins are seen for: (1) thermal stability of protein secondary and tertiary structure (bovine ribonuclease); (2) the rate and extent of enzyme renaturation after acid denaturation (rabbit and shark lactate dehydrogenases); and (3) the reactivity of thiol groups of an enzyme (bovine glutamate dehydrogenase). Attaining osmotic equilibrium with seawater by these fishes has thus involved the selective accumulation of certain nitrogenous metabolites that individually have significant effects on protein structure, but that have virtually no net effects on proteins when these solutes are present at elasmobranch physiological concentrations. These experiments indicate that evolutionary changes in intracellular solute compositions as well as in protein amino acid sequences can have important roles in intracellular protein function.

A modified diacetyl monoxime method for colorimetric determination of urea in soil extracts1

Abstract: Some batches of phosphoric acid contain impurities that affect colorimetric determination of urea in soil extracts by the method of Douglas and Bremner, which involves measurement of the red color formed when an aliquot of extract is heated with diacetyl monoxime and thiosemicarbazide in the presence of phosphoric and sulfuric acid. A modification of this colorimetric procedure is described that permits use of phosphoric acid containing these impurities and allows accurate and precise determination of urea in soil extracts.

The mechanism of passage of endogenous urea through the rumen wall and the role of ureolytic epithelial bacteria in the urea flux

Abstract: 1. The rumen urea concentration in gnotobiotic lambs lacking ureolytic bacteria was equal to that of blood. 2. Bacterial urease (EC 3.5.1.5) activity in sheep fed by intraruminal and intra-abomasal infusion was inversely related to rumen ammonia concentration. 3. A model is proposed for the facilitation and control of urea flux by wall-found ureolytic bacteria.

Biochemical changes in a 100 km run: free amino acids, urea, and creatinine.

Abstract: Free amino acids, urea, and creatinine were analyzed in venous blood and urine of 11 trained (28--81 years old) male subjects before, immediately after, and 1 day after a 100 km running competition. The urinary excretion per minute of all amino acids was lowered after the contest. The renal clearance of creatinine was reduced from 116 to 60 ml/min and the clearance of most amino acids was reduced to a similar extent. However, for the amino acids with a resting clearance under 1 ml/min (x), a high relative clearance ratio (y in % of x) was seen post-exercise: y = -92.3 (log10 x) +23.1, r = -0.83, showing that their high reabsorption capacity had been impaired. Serum concentrations of most free amino acids, including the branched-chain amino acids and alanine, were reduced to 35--85% of the pre-race values. The sulfur amino acids were elevated either at the end of (cystine, to 180%) or 24 h after (methionine, to 155%) the race. Urea production increased by 44% while creatinine production tended to decrease. The production of 3-methylhistidine remained unchanged. These findings are compatible with a stimulation of gluconegenesis at the expense of the amino acid pool without induction of muscle protein catabolism.

The origin of nitrogen incorporated into compounds in the rumen bacteria of steers given protein- and urea-containing diets.

Abstract: 1. Two young Friesian steers fitted with rumen cannulas were each given three different isonitrogenous and isoenergetic diets for successive periods of 2-3 weeks. The diets consisted mainly of straw and tapioca, with the nitrogen supplied mainly as decorticated groundnut meal(DCGM; diet A), in approximately equal amounts of DCGM and urea (diet B), or entirely as urea (diet C). 2. At the end of each period on a given diet, part of the dietary urea of a morning feed was replaced by a solution of [15N]urea which was infused into the rumen. Samples of rumen contents were removed just before giving the 15N dose and at 1,3,5,7 and 24 h afterwards, concentrations of ammonia and its 15N enrichment were determined and samples of mixed bacteria were prepared. Amino acids, ammonia derived mainly from amide groups, and hexosamines were prepared by ion-exchange chromatography of acid-hydrolysates of the bacteria and analysed for 15N. 3. Approximate estimates of net bacterial N synthesis were made from turnover data for rumen fluid and 15N enrichments in rumen fractions. From the determined efficiency of incorporation of urea-N into bacteria recovered at the duodenum, it was calculated that on diets A, B and C respectively 82%, 37% and 0% of the bacterial N was derived from dietary protein or other non-urea sources. 4. [15N]urea was converted rapidly to ammonia and the 15N then incorporated into bacterial amide-N; it appeared at a slower rate in total bacterial non-amide-N. Rates of incorporation into non-amide-N were highest for glutamic acid, aspartic acid and alanine, and generally lowest for proline (pro), histidine (his), phenylalanine(phe), arginine(arg), methionine(met) and galactosamine. A similar ranking was also generally observed for relative 15N abundances (15N atoms % excess in N component divided by 15N atoms % excess in total bacterial N) achieved after several hours. Relative 15N abundances in his, arg and pro increased with decreasing protein (DCGM) in the diet but those in the other protein amino acids, including the poorly labelled met, phe (and its derivative tyrosine) did not. 5. It was concluded that different extents of labelling of the amino acids (at least those present mainly in protein) indicated that different amounts of preformed units (amino acids or peptides) were used. When an adequate supply of such units was available (particularly on diet A) pro, arg, his, met and phe were derived in this way to a greater extent than the other amino acids, but whereas synthesis of pro, arg and his increased on the low-protein diet C, that of met and phe did not. Thus met and phe may be limiting for bacterial growth on diets low in protein and high in non-protein-N. 6. Differences in the extent of labelling of other bacterial N components may be due to different turnover rates.

Fermentation and nitrogen dynamics in Merino sheep given a low-quality-roughage diet

Abstract: 1. Fermentation in the rumen and nitrogen dynamics in the body were studied in mature Merino sheep given a maintenance ration of a low-quality-roughage diet containing mainly chopped wheat straw.2. Intake of metabolizable energy was 3.49 MJ/d and of total N 6.2 g/d.3. From measurements of volatile fatty acid (VFA) production rates and stoichiometric principles, it was calculated that 75% of the digestible organic matter intake was fermented in the rumen, making an estimated 44 g/68d microbial dry matter available to the animal.4. The total flux of ammonia through the rumen NH3 pool, estimated by 15NH3 dilution methods, was 8.2 g N/d of which 3.5 g N/d was irreversibly lost; thus 4.7 g N/d was recycled, partly within the rumen (approximately 3.8 g N/d) and partly via endogenous secretions (approximately 0.9 g N/d). The extensive recycling of NH3-N within the rumen indicated that turnover of microbial N was considerable, and the total production of micro-organisms was at least twice the net outflow.5. The proportion of the N in rumen bacteria derived from rumen ammonia was 62% and thus 38% was derived from other nitrogenous compounds such as peptides and amino acids.6. The rates of transfer of blood urea into the rumen, estimated from the appearance of 14CO2 or 15NH3 in the rumen after intravenous single injections of [14C]-and [15N]urea, did not differ significantly and the mean transfer was 2.3 urea-N/d.7. Estimates of the rate of irreversible loss of urea-C (i.e. urea synthesis in the body) were obtained by analysis of samples of either blood or urine obtained after a single, intravenous injection of [14C]urea. The two methods gave results that did not differ significantly. The estimated rate of urea synthesis in the body was 5.3 g N/d. Urea excretion rate was relatively low, i.e. 1.2 g N/d, and thus transfer of urea to the digestive tract was approximately 4.1 g N/d. Approximately 53% of the latter was transferred to the rumen, and 47% to the rest of the digestive tract. These results are discussed in relation to similar studies with sheep given other diets.8. Various aspects of isotope-tracer methods and the errors that could occur in this type of study are discussed.

Biodegradable polymers: Chymotrypsin degradation of a low molecular weight poly(ester‐urea) containing phenylalanine

Abstract: A low molecular weight poly(ester urea), poly(L-phenylalanine/ethylene glycol/1,6-diisocyanatohexane), and a model diester diurea, dimethyldiphenylalaninehexamethylenediruea, were synthesized and found to be hydrolyzed by α-chymotrypsin solutions at pH 7.8. After ten-day exposure to 0.1 mg/ml enzyme solution at room temperature, 79.9% weight loss was observed for the model diester diurea (containing two ester linkages per molecule). A weight loss of 19.4% was observed for the poly(ester urea) of Mn 1930 (containing an average of eight ester linkages per molecule) after the same period of exposure. A poly(ester urea) of similar molecular weight, but derived from glycine instead of phenylalanine, was found to resist chymotrypsin hydrolysis.

Subunit association and side-chain reactivities of bovine erythrocyte superoxide dismutase in denaturing solvents.

Abstract: The copper- and zinc-containing superoxide dismutase of bovine erythrocytes retains its native molecular weight of 32 000 in 8.0 M urea for at least 72 h at 25 degrees C, as evidenced by sedimentation equilibrium analysis. Subsequent to prolonged exposure to urea, the dimeric enzyme could be dissociated by sodium dodecyl sulfate in the absence of reductants, indicating the absence of unnatural disulfide cross-links. The sulfhydryl group of cysteine-6 was unreactive toward 5,5'-dithiobis(2-nitrobenzoic acid) or bromoacetic acid in both neutral buffer and 8.0 M urea. The histidine residues of the enzyme were resistant to carboxymethylation in neutral buffer and 8.0 M urea. However, when the enzyme was exposed to bromoacetic acid in the presence of 6.0 M guanidinium chloride and 1 mM (ethylenedinitriol)tetraacetic acid (EDTA), both sulfhydryl and histidine alkylation were observed. Guanidinium chloride (6.0 M) increased the reactivity of the sulfhydryl group of cysteine-6 and allowed the oxidative formation of disulfide-bridged dimers. This was prevented by 1 mM EDTA. It follows that 8.0 M urea neither dissociates the native enzyme into subunits nor produces a conformation detectably different than that possessed under native conditions.

Loss of nitrogen and phosphorus in tile drainage as influenced by urea application and grazing animals

Abstract: The effects of urea fertiliser and grazing dairy cattle on the amounts of N and P forms transported in tile drainage from permanent pasture were investigated. In 4 weeks after an application of urea (60 kg N/ha) in July 1975 the increased loss of nitrate (NO3) and total nitrogen (TN) in tile drainage accounted for 2.0 and 2.3% respectively, of the applied fertiliser N. Grazing resulted in a dramatic increase in the concentrations of dissolved inorganic P (DIP) and particulate P (1.5- and 40-fold increases respectively). Concentrations of both NO3 and TN increased 5-fold immediately after grazing, although this effect was less sustained than that caused by urea application. Grazing was of comparable importance to urea application of the loss of NO3 and TN in tile drainage. The greater increase in the loss of particulate P (46.9 g/ha/4 weeks), compared to that of DIP (23.1 g/ha/4 weeks), resulted from a 50% increase in the amount of sediment carried. A 17% reduction in the amount of water discharged after g...

Protein nutrition of growing lambs. 1. Responses in growth and rumen function to supplementation of a low-protein-cellulosic diet with either urea, casein or formaldehyde-treated casein.

Abstract: 1. The effects of supplementation of a cellulose-based diet with either urea, casein or formaldehydetreated (HCHO)-casein were studied in growing lambs. Responses were measured in terms of growth rate, food intake and food conversion ratio.2. In Expt 1 lambs were given free access to a basal diet containing (g/kg) oat-hulls (700) and solka floc (300) (containing 5 g nitrogen/kg dry matter (DM)) supplemented (g/kg basal diet) with either urea (25), untreated casein (75), HCHO-casein (75) or combinations of these. Food intake was increased on average by 27% above that on the basal diet by the addition of either urea, casein, HCHO-casein plus urea. Urea plus HCHO-casein when given as a combined supplement further increased food intake on average by 60% above that on the basal diet. Supplements of either urea, casein, HCHO-casein or casein or casein plus urea changed a mean live-weight loss of 40 g/d on the basal diet to a mean live-weight gain of 56 g/d. Urea plus HCHO-casein further increased lamb growth to 112 g/d.3. In Expt 2 lambs were given free access to the basal diet (plus 25 g urea/kg diet) used in Expt I. In this experiment the content of insoluble and soluble casein in the diets was varied by the addition of HCHO-casein and untreated casein of 0, 150; 50, 100; 100, 50 and 150, o g/kg basal diet respectively. Maximum lamb growth (141 g/d) was obtained with a supplement of 25 g urea plus 100 g HCHO-casein and 50 g casein/kg.4. The growth responses to these supplements suggest a requirement for soluble N by the rumen microorganisms to maximize rumen fermentation, and for maximum growth rate on this diet a further requirement for amino acids produced by protein which has escaped degradation in the rumen.5. Fermentation and the absorption of nutrients were examined in Expt 3 in lambs fitted with simple ‘T’-shaped cannula in the duodenum and ileum, and fed ad lib. one of the diets: a basal diet of oat hulls and solka floc, or the basal diet supplemented (g/kg) with either urea (25), urea plus casein (150), or urea (25) plus HCHO-casein (150). The rates of production of volatile fatty acids (VFA), methane and microbial cells were measured using isotope-dilution techniques. The apparent absorption of nutrients was determined by differences in the quantity of those nutrients in digesta at the duodenum and ileum.6. Supplements of urea, urea plus casein and urea plus HCHO-casein increased organic matter (OM) intake in lambs by 65% above that on the basal diet. OM digestibility was unchanged by the from of nitrogen supplementation. The rates of production of all fermentation end-products varied directly with voluntary food intake.7. Rumen methane production remained constant at 0.09 mol methane/MJ metabolizable energy (ME) intake on all diets, which represented an 11% loss of digestible energy (DE). Hindgut methane production was highest on the urea-supplemented diet.8. The rate of VFA production (mol/MJ ME intake) in the rumen was highest on the diet supplemented with urea in comparison with the basal, urea plus casein and urea plus HCHO-casein diets (which were not significantly different). The molar proportions of the individual VFA in rumen fluid were not significantly different between diets except for the branched chain and higher fatty acids which were highest in proportion with the urea plus casein diet.9. The loss of energy in the faeces, urine or as methane in expired air was not influenced by the form of N supplementation. DE and ME were greater on the supplemented diets, as a result of the increased OM intake of these diets.10. There was no effect of the form of N supplementation on OM digested in the rumen, small intestine or large intestine. Of an increase in OM intake, apparently 55% was digested in the rumen (of which 19% was incorporated into rumen micro-organisms) and 26% disappeared in the small intestines. The apparent digestibility of OM for all diets was 0.67.

Effect of ammonia concentration on the composition, hydrolytic activity and nitrogen metabolism of the microbial flora of the rumen.

Abstract: The mean NH3 concentration in the rumen of sheep fed whole barley (0d8 kg/d) by continuous feeders was increased from 6d1 to 13d4 HIM by supplementing the feed with urea (30 g/kg). This change caused a 90% increase in the rate of degradation of rolled barley, and smaller increases in the rates of degradation of protein and plant fibre in the rumen. The total viable count and numbers of pectinolytic bacteria in rumen fluid increased with the urea supplement. Enzyme studies indicated that NAD-linked glutamate dehydrogenase was the main pathway of NH3 assimilation by rumen bacteria at both NH3 concentrations. Glutamate was the main free amino acid found in the rumen at low NH3 but, despite the low activity of alanine dehydrogenase and glutamate-pyruvate aminotransferase, alanine was the principal amino acid at high NH3 concentrations. Hydrolytic rumen bacteria may require the higher NH3 concentration either for effective NH3 assimilation by an unknown mechanism involving alanine or for full expression of enzyme activity.

The effect of formaldehyde treatment before ensiling on the digestion of wilted grass silage by sheep.

Abstract: 1. Wilted perennial ryegrass (Lolium perenne L. cv. Endura) was ensiled without additive or after addition of a mixture of equal volumes of formic acid (850 g/kg) and formalin (380 g formaldehyde/kg) applied at a rate of 35 g formaldehyde/kg herbage crude protein (nitrogen x 6.25). The digestion of the two silages and the effect of supplemental N as urea or urea plus soya-bean meal on the digestion of the treated silage was studied using sheep fitted with a rumen cannula and re-entrant cannulas in the proximal duodenum and distal ileum. 2. The additive markedly reduced carbohydrate fermentation and protein degradation in the silo. 3. There were no significant differences between diets in rumen pH, dilution rate, volatile fatty acid production and the molar proportions of acetate, propionate and butyrate. However, rumen ammonia levels and the apparent digestibility of organic matter (OM), gross energy (GE) and cellulose in the stomach were significantly depressed (P less than 0.05) by the additive. It also reduced (P less than 0.05) the extent to which the N of the silage was degraded in the rumen and, with the treated silage, more microbial N was synthesized in the rumen than food N degraded, resulting in a net grain of N between mouth and duodenum, as compared to a net loss with the untreated silage. 4. Supplementation of the treated silage with urea or urea plus soya-bean meal significantly increased (P less than 0.05) the amount of food N degraded in the rumen and rumen ammonia levels but had no effect on the apparent digestibility of OM, GE and cellulose in the stomach or on the amount of microbial N reaching the duodenum. 5. The quantity of microbial amino acids entering the small intestine and the apparent digestibility of amino acids in the small intestine were similar for all four diets. However, the quantity of food amino acids reaching the small intestine was significantly higher with the three diets containing the treated silage and consequently the apparent absorption of amino acids from the small intestine was substantially higher with these diets than with the untreated silage.

Thixotropic coating agents based on urea adduct of polyamine and monoisocyanate

Abstract: A thixotropic coating agent, more especially a binder or coating composition, based on a mixtrue of conventional binder-containing systems, optionally in admixture with liquid solvents or diluents, and a thixotropizing agent containing urea groups, wherein the thixotropizing agent is, in part at least, a urea adduct obtained by reacting (a) primary and, optionally, secondary polyamines, (b) monoisocyanate compounds and, optionally, (c) diisocyanate compounds in the presence of at least part of the binder.

The uptake of urea by the diatom, phaeodactylum

Abstract: Summary Urea-grown cells of Phaeodactylum absorbed [14C]urea by an active mechanism. Most of the urea taken up was present in the cells as free urea and the ratio of internal to external concentration could exceed 3000. The activity of the transport mechanism was greatly increased by depriving the cells of nitrogen for up to 24 h. The uptake mechanism had a high affinity for urea, the half-saturation constant being about 1·0 μM. Active uptake of urea occurred in darkness, particularly in nitrogen-deprived cells, but uptake was markedly stimulated by light. Uptake was not inhibited by DCMU but was abolished almost completely by 10−4m CCCP. It is concluded that active uptake is driven by phosphorylation. Uptake of [14C]urea continued until a constant level within the cells was attained, the plateau value probably resulting from a balance between rate of active uptake and rate of passive loss by diffusion. The transport mechanism was absent from cells grown with ammonium as nitrogen-source. The urea uptake mechanism developed in such cells when they were deprived of nitrogen; cycloheximide prevented the development of the mechanism. The mechanism was lost when urea-grown cells were incubated in ammonium medium for 24 h but ammonium (at concentrations up to 10 mM) did not inhibit short-term uptake of urea into urea-grown cells.

Nitrogen metabolism in Brahman cross, buffalo, banteng and Shorthorn steers fed on low-quality roughage

Abstract: Urea metabolism was studied in Brahman cross, buffalo, banteng and Shorthorn cattle offered a low quality hay. Intravenous injections of [I4C]urea and 51Cr-~~~~ were used to determine the irreversible loss of urea from the plasma, the degradation of urea in the rumen and lower digestive tract, and the glomerular filtration rate. When species were compared at equal liveweights and nitrogen intakes, buffaloes had significantly higher (P < 0.05) plasma urea concentrations and rates of irreversible loss of urea carbon from plasma than the other species. There were no significant differences between species in urinary urea excretion. Urea degradation in the digestive tract was linearly related to the irreversible loss of urea, and the proportion of irreversible urea loss degraded was significantly (P < 0.05) lower in Shorthorn cattle (48 %) than in the other species (73-91 %). Shorthorn cattle reabsorbed urea from the glomerular filtrate with a lower efficiency (60%) than did the other species (85-94%). In Brahman cross, buffalo and banteng, plasma urea recycled to the rumen was a relatively constant amount (4.3 g nitrogenld) and represented on average 39% of the urea degraded in all parts of the digestive tract. Urea degraded in the digestive tract increased linearly with increasing irreversible loss of urea from plasma. It was concluded that, despite significant differences between species in urea synthesis and degradation, there was little indicatation that these differences constituted a significant nitrogen conservation mechanism in any one species.

A simple technique to estimate severity of stress.

Abstract: A simple procedure to estimate stress has been developed based upon 24 hour urine urea nitrogen excretion. This catabolic index partitions total urea excretion into that resulting from dietary protein intake and obligatory urea excretion and that due to an increase in endogenous protein catabolism: catabolic index equals 24 hour urine urea nitrogen excretion - (0.5 dietary nitrogen intake + 3 grams) where an index of less than zero represents no significant stress; an index of zero to 5, moderate stress, and an index greater than 5, severe stress. In 111 persons, significant differences were noted in the catabolic index, reflecting varying degrees of stress, nutrient intake and nutritional status. The catabolic index may have useful diagnostic and treatment applications.

Protein nutrition of growing lambs. 2. Effect on nitrogen digestion of supplementing a low-protein-cellulosic diet with either urea, casein or formaldehyde-treated casein.

Abstract: 1. Lambs with cannulas in the duodenum and ileum were allowed free access to one of four diets: a basal diet of oat hulls and solka floc, or the basel diet supplemented with either urea, urea plus casein or urea plus formaldehyde-treated (HCHO)-casein. Mean nitrogen intake was 1.9 g N/d for the basal diet and 15.0. 32.4 and 36.9 g N/d respectively for the other diets. 2. The rate of irreversible loss of ammonia from the rumen pool estimated using 15NH4+ was highest on the casein diet (33 g NH3-N/d) by comparison with 18 g NH3-N/d for the urea and HCHO-casein diets and 7 g NH3-N/d for the basal diet. 3. The proportions of bacterial and protozoal N in the rumen derived from rumen ammonia did not differ significantly between the supplemented diets and were 0.66 and 0.52 respectively. 4. Estimation of 15N flowing to the duodenum during continuous infusions of 15NH4+ into the rumen indicated considerable ammonia absorption from the rumen on all the diets. Greatest absorption of ammonia (21 gN/d) apparently occurred in animals on the diet supplemented with urea and casein. 5. The estimated microbial non-ammonia-N (NAN) flowing out of the rumen per unit organic matter fermented in the rumen (FOM) was similar on all diets, i.e. 21.3 (+/- 1.09) g N/kg Fom. the requirement for dietary fermentable N for microbial N production on these diets was 1.2 (+/- 0.07) g N/MJ ME. 6. The flow of NAN into the duodenum and through the ileum, and total N in the faeces was significantly influenced by the form of N supplementation. The flow of NAN into the duodenum for the HCHO-casein diet (27 g N/d) was more than twice that for the other diets (11 g N/d). The flow of NAN through the ileum and excretion of total N in the faeces was also greater with the HCHO-casein diet than with all other diets. The apparent digestibility of NAN in the small intestine ranged between 0.62--0.66 for all diets. 7. Urea and casein supplements were apparently completely degraded in the rumen. In contrast, the HCHO-casein was almost completely resistant to degradation in the rumen and only 65% of the HCHO-casein was digested in the small intestine. 8. Protein absorbed : energy absorbed (expressed as NAN digested in the small intestine/MJ ME) was calculated to be 5.5 (+/- 0.70) for the basal, urea and urea-plus-casein diets, and 11.6 (+/- 1.71) for the urea-plus-HCHO-casein diet.

Nutritive value of potato crude protein as influenced by manuring and amino acid composition.

Abstract: Potatoes were grown in pots and fertilised with varying amounts of nitrogen (as nitrate or ammonium sulphate or urea), phosphorus, potassium and cow manure. The largest yield, 451 g DM per pot, was obtained with nitrogen in the form of urea. N-applications and P- and K-deficiency in the soil increased the total-N content, which varied from 1.14–3.07%. Concentrations of nitrate-N (0.001–0.016%) were negligible. Increasing N-concentrations were associated with decreases in the crude protein of most amino acids including lysine (6.26–4.17%), threonine (4.08–2.90%), methionine (1.98–1.46%) and tryptophan (1.74–0.86%). The concentrations of aspartic and glutamic acids (probably mainly present as their amides) increased. Differences in amino acid composition between boiled and unboiled potatoes were negligible. From 70 to 90% of the decrease in concentration of most essential amino acids could be accounted for by changes in N-content of dry matter. Phosphorus and potassium affected the amino acid composition indirectly through their effects on N-content. In rat feeding experiments increasing N-concentrations in potatoes increased the true digestibility of the crude protein from 79 to 91 but decreased the biological value from 82 to 59. The net protein utilisation did also decrease (from 67 to 54). These relationships were linear below 2.2% N in dry matter. Changes were mainly dependent on variations in N-content. Decreases in essential amino acid indices or chemical scores were closely reflected in the results of the feeding experiments. The true amino acid digestibilities were different for individual amino acids and increased with increasing N-concentration in dry matter.

Appearance of 15N-labeled intestinal microbial amino acids in the venous blood of the pig colon.

Abstract: Two experiments were done to determine whether pigs possess the ability to absorb amino acids synthesized from urea nitrogen by indigenous microbes in the large intestine. Incorporation of [15N]urea into amino acid fractions of bacterial cells from the rectum and of the deproteinized incubated medium were examined in an experiment in vitro. The isotope was incorporated into 17 amino acids and the ammonia fraction of these samples. The absorption of the microbial amino acids from the colon was investigated by determination of the 15N concentration of the free amino acids in the venous blood of the colon after infusion of the 15N-labeled microorganisms into the cecum. The increase of 15N concentration was also observed in the plasma-free amino acids (threonine, isoleucine, phenylalanine, lysine, histidine, arginine, aspartic acid, serine, alanine, cystine) of the blood from the colic branch of the ileocolic vein. The results of these experiments indicated that pigs have the ability to utilize the microbial amino acids synthesized from urea nitrogen in the large intestine.