Loss Of Lysine Research Articles

Site specificity of glycation and carboxymethylation of bovine serum albumin by fructose

We report an investigation of the site specificity, extent and nature of modification of bovine serum albumin (BSA) incubated with fructose or glucose at physiological temperature and pH. Sites of early glycation (Heyns rearrangement products (HRP) from fructose; fructoselysine (FL) from glucose) as well as advanced glycation (N(epsilon)-(carboxymethyl)lysine; CML) were analyzed by liquid chromatography-mass spectrometry. The major site of modification by fructose, like glucose, is Lysine-524 and this results in, respectively, 31 and 76% loss of the corresponding unmodified tryptic peptide, Gln525-Lys533. In addition, total lysine, HRP, FL, CML and N(epsilon)-(carboxyethyl)lysine in the incubations, was quantified. Almost all of the loss of lysine in the fructose-modified BSA was attributed to the formation of CML, with the yield of CML being up to 17-fold higher than glucose-modified BSA. A mechanism for the formation of CML from the HRP is proposed.

Technological properties and non-enzymatic browning of white lupin protein enriched spaghetti

Spaghetti was prepared by replacing semolina with different amounts of lupin protein, in order to increase the protein content. A detailed investigation of the rheological properties of the dough and the cooking quality of pasta was performed in comparison to standard semolina spaghetti. Moreover, the effect of the addition of lupin protein on non-enzymatic browning was evaluated by measuring ε-furoylmethyllysine (furosine) and 5-hydroxymethyl-2-furancarboxaldehyde (HMF), which are considered useful indices of semolina quality and pasta processing conditions. Dried spaghetti fortified with 5% of lupin protein isolate has a colour and rheological features comparable with the semolina sample and also the behaviour during cooking results to be satisfactory. As far as the thermal damage is concerned, the furosine values of fortified spaghetti differ only marginally from standard pasta and the percentage lysine loss is quite small (ranging from 12.1% to 15.7%).

Histone H3 lysine 9 and H4 lysine 20 trimethylation and the expression of Suv4-20h2 and Suv-39h1 histone methyltransferases in hepatocarcinogenesis induced by methyl deficiency in rats

The field of cancer epigenetics has received much attention in recent years. However, the relationship of cancer epigenetics with cancer etiology is not clear. Recent studies suggest the involvement of altered DNA methylation and histone modifications in the emergence of epigenetically reprogrammed cells with specific tumor-related phenotypes at premalignant stages of tumor development. In this study, we used a methyl-deficient model of rodent hepatocarcinogenesis to examine the roles of DNA, histone H3 lysine 9 and histone H4 lysine 20 methylation, and the level of the expression of Suv39h1 and Suv4-20h2 histone methyltransferases in the carcinogenic process. We demonstrated that the development of liver tumors was characterized by progressive demethylation of DNA repeats, decrease in histone H4 lysine 20 trimethylation, and a gradual decrease in the expression of Suv4-20h2 histone methyltransferase. A prominent increase in the trimethylation of histone H3 lysine 9 and in the expression of Suv39h1 histone methyltransferase was observed in preneoplastic nodules and liver tumors indicating the promotional role of these epigenetic alterations at later stages of carcinogenesis. The appearance of tumor-specific epigenetic alterations (demethylation of repetitive elements, loss of histone H4 lysine 20 trimethylation, altered expression of Suv4-20h2 and Suv39h1 histone methyltransferases) at preneoplastic stages of hepatocarcinogenesis provides experimental support for the epigenetic hypothesis of tumorigenesis that considers stress-induced epigenetic reprogramming of the cell as an important prerequisite to succeeding mutations.

The effect of controlled fermentation on the fate of synthetic lysine in liquid diets for pigs

Crystalline lysine is frequently added to pig diets to provide the correct amino acid balance. Recent studies have shown that free lysine can be lost when liquid pig feed is fermented with lactic acid bacteria (LAB). The metabolism of lysine was examined, over 72 h, in uninoculated liquid feed (Control) and in liquid feed inoculated with lactic acid bacteria (LAB) ( Lactobacillus plantarum and Pediococcus acidilactici); or Escherichia coli and combinations of LAB and E. coli. In the Control and the fermentations that included E. coli, lysine was rapidly metabolised, with ca. 90% degraded in 21 h. The production of cadaverine accounted for ca. half of the lysine lost. There was no loss of lysine in the LAB fermentations and no cadaverine was produced. Combining E. coli and LAB resulted in a loss of ca. 20% lysine in the first 7 h with no further metabolism thereafter. Cadaverine produced in these fermentations accounted for all of the lysine lost. The rate of lysine metabolism was inhibited by the increase in lactic acid present in the fermentations. Fermenting E. coli and LAB with the addition of 50 mM lactic acid at 0 h resulted in the lysine levels remaining unaltered throughout the fermentation period. These results imply that the loss of lysine from fermented liquid pig diets is due to the metabolism of lysine by E. coli before they are eliminated from the diet by the increasing acidity resulting from LAB fermentation.

Loss of DNA methylation and histone H4 lysine 20 trimethylation in human breast cancer cells is associated with aberrant expression of DNA methyltransferase 1, Suv4-20h2 histone methyltransferase and methyl-binding proteins

Cancer cells are characterized by epigenetic dysregulation, including global genome hypomethylation, regional hypo- and hypermethylation, altered histone modifications, and disturbed genomic imprinting. Despite the long-established fact that global DNA hypomethylation is a common feature of tumors, very little is known about evolution of this and other epigenetic alterations during tumor progression. The present study was undertaken to characterize the status of epigenetic dysregulation in three human breast cancer cell lines (MCF-7, MDA-MB-231 and MDA-MB-231(S30) that represent different stages of human breast cancer. Our data show that breast cancer cells are characterized by significant alterations in cellular epigenetic status compared to non- tumorigenic MCF-10-2A epithelial breast cells. Interestingly, more malignant MDA-MB- 231 human breast cancer cells have a more prominent loss of DNA methylation accompanied by altered expression of maintenance DNA methyltransferase DNMT1, methyl-binding proteins MeCP2 and MBD2, decreased trimethylation of lysine 20 of histone H4 and hyperacetylation of histone H4 compared to MCF-7 cells. The decrease in trimethylation of lysine 20 of histone H4 in MDA-MB-231 cells was accompanied by diminished expression of Suv4-20h2 histone methyltransferase. The results of present study demonstrate that MDA-MB-231 cells have more extensive epigenenic alterations than MCF-7. These results demonstrate that human breast cancer cells are characterized by prominent epigenetic alterations which are associated with increased malignant properties of cancer cells. Such epigenetic dysregulation may contribute to and may be indicative of the formation of a more aggressive tumor phenotype during tumor progression.

Available lysine content in human milk: Stability during manipulation prior to ingestion

Available lysine content is an indicator of protein quality and nutritional value of milk. Many studies have examined the effects of extraction, treatment and storage of human milk upon its components, though no references are found regarding the possible changes in milk quality as defined by its content in essential amino acids such as lysine. The present study investigates the available lysine content in human milk and the variations in lysine resulting from milk manipulation as follows: (a) Cold storage (refrigeration at 4 degrees C for 48 hours, and frozen for 15 days at -20 degrees C); (b) Thermal treatment under conditions of low (Holder)(63 degrees C/30 minutes) and high pasteurization (75 degrees C/15 seconds). The results obtained show a decrease in milk lysine concentration after storage in both refrigerated and frozen samples. Pasteurization causes a highly significant loss of available lysine. The lysine losses were greater on applying low pasteurization versus the more gentle conditions of high pasteurization. While manipulation through cold storage or thermal treatment does not affect the protein content of human milk, its protein quality is modified. When human milk must be subjected to hygienization, it is preferable to apply high temperature treatment (75 degrees C, 15 seconds) than habitual pasteurization (63 degrees C, 30 minutes).

Effects of graded levels of soya-bean protein on endogenous ileal lysine loss and amino acid digestibility in growing pigs

AbstractThis experiment investigated the effects of feeding graded levels of a soya-bean protein product (HP300, Hamlet Protein A/S Company, Denmark) on endogenous ileal lysine loss, apparent ileal amino acid digestibility, standardized true ileal amino acid digestibility determined using the protein-free (PF) method, and real ileal amino acid digestibility determined using the homoarginine (HA) method. The soya-bean protein product was obtained by purifying and defattening soya bean via a proprietary microbial process that decreased the level of trypsin inhibitors and other anti-nutritional factors in soya bean. Six barrows, with an initial body weight of 37·4 ± 1·3 kg, were surgically fitted with simple T-cannulae at the distal ileum and offered six maize-starch-based diets according to a 6 × 6 Latin-square design. The six diets were formulated to provide 0, 50, 100, 150, 200, or 250 g crude protein (CP) per kg by dietary inclusion of 0, 90, 182, 274, 367 or 460 g/kg of soya-bean protein. Five kg of soya-bean protein product was guanidinated in order to estimate endogenous amino acid flow and real ileal amino acid digestibility. Chromium III oxide (5 g/kg) was included in the non-guanidinated diets while dysprosium chloride (0·1 g/kg) was included in the guanidinated diets as an indigestible marker. The experimental periods lasted 8 days. On day 6 of each period, ileal digesta was collected for 24 h to determine apparent and standardized true ileal amino acid digestibility of the non-guanidinated diets. At 08:00 h on day 8, the pigs were given a single meal of the diets containing guanidinated protein and their ileal digesta was collected for 24 h in order to determine the total HA flow and the real ileal digestibility of lysine. Endogenous ileal lysine flow appeared to follow a sigmoid curve starting at about 370 mg/kg dry matter (DM) intake for pigs given the PF diet and continuing asymptotically to about 750 mg/kg DM intake when the inclusion level of the soya-bean protein product was increased to 182 g/kg (100 g/kg of CP). The endogenous ileal lysine flow for pigs given the PF diet was similar (P > 0·05) to that of pigs given 90 g/kg soya-bean protein (50 g/kg of CP) and it increased sharply (P < 0·05) as the level of soya-bean protein increased from 90 to 182 g/kg (50 to 100 g/kg of CP). Thereafter, it was relatively constant (P > 0·05). With an increase in soya-bean protein, there was a quadratic increase (P < 0·01) in the apparent ileal digestibilities for all amino acids except valine and phenylalanine. Standardized true ileal amino acid digestibility decreased (P < 0·05) with an increase in soya-bean protein level. However, real ileal amino acid digestibilities were not influenced (P > 0·05) by soya-bean protein in the diet at levels between 90 and 367 g/kg (50 and 200 g/kg of CP). In conclusion, endogenous ileal lysine flow was not constant and was significantly affected by soya-bean protein level. The results of this study suggest that standardized true ileal amino acid digestibility should be measured between 100 and 200 g/kg of CP (182 and 367 g/kg soya-bean protein) while real ileal amino acid digestibility is unaffected by protein levels between 50 and 200 g/kg of CP (90 and 367 g/kg soya-bean protein).

The role of loop ZA and Pro371 in the function of yeast Gcn5p bromodomain revealed through molecular dynamics and experiment

Biological experiments were combined with molecular dynamics simulations to understand the importance of amino acidic residues present in the bromodomain of the yeast histone acetyltransferase Gcn5p. It was found that residue Pro371 plays an important role in the molecular recognition of the acetylated histone H4 tail by Gcn5p bromodomain. Crystallographic analysis of the complex showed that this residue does not directly interact with the histone substrate. It has been demonstrated that a double mutation Pro371Thr and Met372Ala in the Gcn5p bromodomain impairs chromatin remodeling activity. It is demonstrated here that, in this double mutant and in the fully deleted bromodomain strain, there is lower growth under amino acid deprivation conditions. By in vitro surface plasmon resonance (Biacore) experiments it is shown that the binding affinity of the double mutation to acetyl lysine 16 histone H4 peptide decreases. Molecular dynamics simulations were used to explain this loss in acetyl lysine-Gcn5p bromodomain affinity, in the double mutant. By comparing nanosecond molecular dynamics trajectories of the native as well as the single and doubly mutated bromodomain, it is concluded that the presence of Pro371 is important to the functionality of the Gcn5p bromodomain. In the simulation a point mutation involving this highly conserved residue induced an increase in the flexibility of the ZA loop, which in turn modulated the exposure of the binding pocket to the acetyl lysine. The combined double mutations (Pro371Thr-Met372Ala) not only markedly perturb the motion of the ZA loop but also destabilize the entire structure of the bromodomain.

Available lysine and fluorescence in heated milk proteins/dextrinomaltose or lactose solutions

In order to predict and compare the effects of dextrinomaltose and lactose on available lysine loss by the Maillard reaction, six model systems were prepared by mixing casein, laboratory whey protein or commercial whey protein with dextrinomaltose or lactose. The solutions were prepared at concentrations similar to those used in enteral and infant formula processing and were heated at 100, 120 or 140 °C for 0–30 min. The progress of the Maillard reaction in these model systems was followed by monitoring free fluorescence intermediary compounds. Model systems with lactose showed higher available lysine less than the model systems with dextrinomaltose; linear lysine losses were obtained between 0 and 20 min at 100 and 120 °C. At sterilization temperature and time (120 °C/10 min), lysine losses of milk proteins with dextrinomaltose as reducing sugar were 6.1% for casein, 4.1% for laboratory whey protein and 13.4% for commercial whey protein. Available lysine showed correlation with furosine in model systems prepared with lactose and casein or laboratory but not commercial whey protein at 100 and 120 °C. The initial fluorescence value obtained by mixing casein or laboratory whey protein with lactose or dextrinomaltose was low (between 3.8 and 5.7), whereas the value obtained when commercial whey proteins were used was close to 9. At 120 °C/10 min, there was only a small increase of fluorescence in casein and laboratory whey protein but a large increase in commercial whey protein (threefold the initial value). Fluorescence measurement is useful for finding the extent of the Maillard reaction in commercial whey protein (thermally damaged protein). An absolute value greater than 10 may indicate that products were prepared with thermally damaged proteins.

Loss of available lysine during processing of different dulce de leche formulations

Dulce de leche is a dairy‐based confectionery product prepared by heat concentration of milk and sugar, which can be partially replaced by other sugars. The effect of different formulations commonly used in the manufacture of this product on the rate of available lysine loss by Maillard reactions was examined. The replacement of 10% of sucrose by glucose increased by 90% the rate of lysine glycation, while the rise with fructose was only 30%. The use of skim milk led to a low fat product with the same available lysine content as the traditional one. Dulce de leche prepared with lactose‐hydrolysed milk had a very low available lysine value.

Effect of supercritical carbon dioxide treatment on the Maillard reaction in model food systems

The effect of supercritical carbon dioxide treatment on the development of the Maillard reaction in powdered model systems of lactose/ovine caseinmacropeptide and lactose/β-lactoglobulin at different pH values was studied. Supercritical carbon dioxide treatments in static conditions at 30 MPa and 50 °C for up to 5 h were applied to model systems. Control experiments at 50 °C were also performed. All assayed model systems treated with carbon dioxide under supercritical conditions showed lower extent of the Maillard reaction than control treated samples. Differences between supercritical carbon dioxide treated and control samples increased with pH. These results indicate that supercritical carbon dioxide treatment of food samples does not favour the Maillard reaction and thus can be applied in foods that may require special care to avoid excessive loss of available lysine.

Targeted Deletion of the Chicken β-Globin Regulatory Elements Reveals a Cooperative Gene Silencing Activity

The chicken beta-globin locus represents a well characterized system to study the role of both proximal and distal regulatory elements in a eukaryotic multigene domain. The function of the chicken beta(A)/epsilon-intergenic enhancer and upstream regulatory elements 5'-HS1 and 5'-HS2 were studied using a gene targeting approach in chicken DT40 cells followed by microcell-mediated chromosome transfer into human erythroleukemia cells (K562). These regulatory elements all repressed expression of the rho- and beta(H)-chicken globin genes in the chromosome transfer assay. No rho- or beta(H)-globin gene expression was detected in K562 cells containing the chicken chromosome without deletions, whereas rho- and beta(H)-mRNA was activated in K562 cells containing chicken chromosomes with deletions of the intergenic enhancers, 5'-HS1 and 5'-HS2. Transcriptional activation of the rho- and beta(H)-globin genes correlated with hyperacetylation of histones H3 and H4, loss of histone H3 lysine 9 methylation, and binding of RNA polymerase II to the gene promoters. Surprisingly, the status of CpG dinucleotide methylation at the promoters did not correlate with the transcriptional status of the genes. Our results using a chromosomal transfer assay demonstrate an identical silencing function for these regulatory elements, which suggests they function as part of a common silencing pathway or complex.

Total and Reactive Lysine Contents in Selected Cereal-Based Food Products

The aim of the study was to determine and compare reactive and total lysine contents in a range of breakfast cereal products. Crude fiber, fat, ash, and crude protein contents of 20 breakfast cereal products ranged from 4 to 38, 14 to 144, 7 to 32, and 52 to 253 g/kg, respectively. The concentrations of glutamic acid (18.7-32.1 g/100 g protein) and proline (4.7-10.8 g/100 g protein) were high while those of the amino acids methionine (1.2-2.0 g/100 g protein) and histidine (1.2-3.3 g/100 g protein) were relatively low. There was a strong relationship between reactive lysine determined using the guanidination and fluorodinitrobenzene methods (R = 0.99). The total lysine content, determined after conventional acid hydrolysis, ranged from 0.8 to 3.7 g/100 g protein, while the reactive lysine content (guanidination) ranged from 0.4 to 2.8 g/100 g protein. Reactive lysine was 20-54% lower than total lysine in the cereal products. The large differences between total and reactive lysine suggest a considerable loss of lysine in the breakfast cereals tested.

Colour measurement as indicator for controlling the manufacture and storage of enteral formulas

Reflectance colour measurement was used to control the browning reaction during the manufacture (untreated, UHT, standardisation and bottle sterilisation) and storage (4, 20, 32 and 55 °C from 1 to 36 weeks) of two types of enteral formula (3.7% and 5.4% protein). Precision studies showed coefficients of variation of 0.19%, 4.77% and 1.02% for L ∗, a ∗ and b ∗ parameters respectively. The a ∗ and b ∗ parameters proved useful to monitor the manufacture of these products. No statistically significant changes were observed during storage at 4 °C. At 55 °C the parameters a ∗ and b ∗ increased for both types of formula. However, at 20 and 32 °C, the a ∗ parameter was useful for the formula with 3.7% protein and the b ∗ parameter for that with 5.4%. Colour measured as reflectance was strongly correlated with colour absorbance at 420 nm, especially during storage at 20 °C. Likewise, a strong correlation was observed between nutritional value (measured as lysine loss) and colour. Colour measurement is a simple and fast method to control different processing and storage conditions of enteral formulas, and may also be useful as an indirect measurement of nutritional value.

Chemical Indicators of Heat Treatment in Fortified and Special Milks

Carbohydrate and furosine contents in 12 commercial fortified and special milk samples (pasteurized goat's and ewe's milks; ultrahigh-temperature (UHT) goat's milk, UHT milks fortified with calcium, magnesium, fiber, or royal jelly and honey; and lactose-hydrolyzed milks) were analyzed. Except for lactose-hydrolyzed milks, furosine, lactose, lactulose, galactose, glucose, N-acetylgalactosamine, N-acetylglucosamine, and myo-inositol contents were similar to the previously reported values for UHT or pasteurized milk samples. In lactose-hydrolyzed milks, lactulose was not detectable and lactose was present in low amount; high levels of glucose, galactose, fructose, tagatose, and furosine were also detected in this type of milk. Results found in commercial milks were compared to those obtained in laboratory-prepared UHT milks with lactose hydrolyzed prior to heating. Hydrolysis of lactose before thermal treatments promoted elevated accumulation of reducing sugars (galactose and glucose) that could be partially converted to the corresponding isomers (tagatose and fructose) during heating. In addition, the reducing sugars could also react with the amino groups of proteins, giving rise to the corresponding Amadori compound. According to the obtained results, heating prior to hydrolysis of lactose is suggested to avoid a considerable loss of available lysine.

Digestible Reactive Lysine in Selected Milk-Based Products

Reactive lysine contents, true ileal reactive lysine digestibility, and true ileal digestible reactive lysine contents were determined in a wide range of processed milk products. A previously validated assay based on determining reactive lysine in both food and ileal digesta, after reaction of these materials with O-methylisourea, was applied. Semisynthetic diets containing milk products as the sole sources of protein and including chromic oxide as an indigestible marker were fed to growing rats. Digesta from the terminal ileum were collected posteuthanasia and, with samples of the diets, analyzed for reactive lysine (homoarginine) contents. True reactive lysine digestibility was determined after correcting for endogenous lysine loss at the terminal ileum of rats fed an enzyme hydrolyzed casein-based diet, followed by ultrafiltration (5000Da) of the digesta. Digestible total lysine (determined using conventional methods) was also determined. The true ileal reactive lysine digestibility was high (>91%) in all the milk products tested, but was highest in the UHT milk (100%) and lowest in the infant formulas (91 to 93%). Total lysine digestibility (conventional measurement) significantly underestimated reactive lysine digestibility for all the products tested. The mean underestimation ranged from 1.3 to 7.1% units. The mean digestible total lysine content was significantly different from the available lysine content for most of the products examined. In some cases this difference was small (<3%), but for a number of the products (evaporated milk, whole milk protein, lactose hydrolyzed milk powder, and a sports formula) the difference was greater (6.5 to 14%). This would suggest firstly that total lysine and total lysine digestibility determined using conventional methods were inaccurate when applied to some milk-based foods, and secondly that some of the milk products have undergone lysine modification. In general, milk proteins are a highly digestible source of amino acids and lysine.

RNA helicase A is important for germline transcriptional control, proliferation, and meiosis in C. elegans

RNA helicase A (RHA) is a multifunctional protein with established roles in chromatin regulation. The protein is conserved in worms, Drosophila, and mammals, but its role in worms has not been previously studied. We found that a deletion mutant lacking rha-1 has a temperature-sensitive defect in germline transcriptional silencing, consistent with RHA-1 having a function in transcription regulation. Transcriptional desilencing in these rha-1( tm329) mutants was associated with a loss of lysine 9 methylation on histone H3 that is normally associated with silenced chromatin. Other histone modifications are also mis-localized in the germ cells in the mutants. These defects in histone modifications suggest that there is a general transcription regulation defect in the mutant worms that results in a temperature-sensitive sterile phenotype. At the restrictive temperature, the extent of germ cell mitoses is reduced, and the mutants are sterile due to defects in meiosis and gametogenesis. Our results suggest that RHA-1 is a conserved transcription regulation protein that controls germline proliferation and development in C. elegans.

Amino acid composition of spring wheats and losses of lysine during chapati baking

Forty-four spring wheat varieties representing 64 years of wheat cultivar releases were evaluated for amino acid composition. The concentration of several amino acids differed among the wheat varieties but amino acids did not significantly consistently among wheat varieties and growth conditions. Significant differences existed in amino acid score due to wheat varieties and crop years. The variations in amino acids (g/100 g flour) were found in lysine 0.255–0.392, leucine 0.449–0.927, isoleucine 0.224–0.492, threonine 0.277–0.516, valine 0.288–0.587, methionine 0.072–0.160, histidine 0.118–0.265, arginine 0.149–0.643, alanine 0.036–0.119, aspartic acid 0.453–0.841, glutamic acid 0.743–1.313, glycine 0.393–0.753, proline 0.851–1.420, serine 0.409–0.722 and tyrosine 0.189–0.597. The chapatis contained on average lysine 0.261, leucine 0.542, isoleucine 0.277, threonine 0.353, valine 0.359, methionine 0.101, histidine 0.159, arginine 0.285, alanine 0.063, aspartic acid 0.618, glutamic acid 0.844, glycine 0.526, proline 1.088, serine 0.538 and tyrosine 0.283 (g/100 g). The wheat varieties Punjab 96, Shahkar 95, Inqulab 91 and C518 contained relatively higher concentration of different amino acids as compared to other wheat varieties. Loss in content of amino acids was observed during baking of chapatis. The decline in lysine content ranged from 1.11% to 23.58% during chapati baking (12.4% protein basis). The amino acid scores in wheat varieties and chapatis were 45 and 40, respectively. The mean crude protein content in chapatis was 11.85%.

Renal Arginine Metabolism

The kidney plays a major role in arginine metabolism in 3 principal ways: arginine synthesis, creatine synthesis, and arginine reabsorption. Appreciable quantities of arginine are synthesized in the kidney from citrulline produced by the intestine. The renal enzymes of arginine synthesis, argininosuccinate synthetase and argininosuccinate lyase, occur in the cells of the proximal tubule. The rate of arginine synthesis depends on citrulline delivery and does not appear to be regulated by dietary arginine availability. Renal arginine synthesis in humans produces approximately 2 g arginine/d, which may be compared to an intake, from a Western diet, of approximately 4 to 5 g/d. Spontaneous, nonenzymatic breakdown of creatine and creatine phosphate to creatinine causes the excretion of 1 to 2 g creatinine/d and requires the replacement of an equivalent amount of creatine from the diet and by endogenous synthesis. The first enzyme of creatine biosynthesis, L-arginine:glycine amidinotransferase, occurs in the kidney and produces guanidinoacetate, which is released into the renal vein. The renal output of guanidinoacetate, however, is rather low, and we propose that the entire pathway of creatine synthesis may also occur in the liver. Renal arginine reabsorption salvages approximately 3 g arginine/d. At the apical membrane of proximal tubular cells, arginine shares a transporter with lysine, ornithine, and cystine. Defects in this heteromeric transporter cause cystinuria, which is also characterized by urinary loss of arginine, lysine, and ornithine. Arginine is transported out of the proximal tubular cells at the basolateral membrane by another heteromeric transporter, which also transports lysine and ornithine. Defects in this transporter cause lysinuric protein intolerance.

Effect of pre‐treatment and smoking process (cold and hot) on chemical, microbiological and sensory quality of mackerel (Scomber scombrus)

AbstractThe sensory, hygienic, toxicological and nutritional profiles of hot‐ and cold‐smoked mackerel samples were studied with various pre‐treatments. The panellists assessed all smoked samples as barely to quite acceptable products whilst the product immersed in 120 g kg−1 sodium chloride and 60 g kg−1 fructose prior to smoking was assessed as very acceptable regarding its sensory characteristics. The available lysine in all hot smoked samples was reduced to the same extent (32%) whilst a very good correlation (r = 0.912) was observed between loss of available lysine and colour formation of the cold‐smoked products, indicating the high contribution of lysine in the interactions with carbonyls. Histamine was found in highly unacceptable levels even in the unprocessed samples (600 mg kg−1) and strongly increased (2220 and 2250 mg kg−1) in the cold‐ and hot‐smoked samples, respectively, due to all treatments. These are levels which would be expected to cause symptoms of scombrotoxin poisoning. Benzo(a)pyrene, fluoranthene and perylene were at high levels both in cold‐ (2.1, 4.3 ± 0.04 and 7.2 ± 0.05 µg kg−1) and hot‐smoked samples (9.2, 7.8 ± 0.03 and 9.4 ± 0.14 µg kg−1, respectively) and were, as expected, influenced by the temperature. The aerobic bacteria remained at acceptable levels, since salt and high temperature prevent bacterial growth. Copyright © 2004 Society of Chemical Industry