Nutritional value of protein hydrolysis products (Oligopeptides and free amino acids) as a consequence of absorption and metabolism kinetics

When pigs were submitted to duodenal infusion of solutions containing a large percentage of small peptides (PEP) or free amino acids with the same pattern (AAL) amino acids appear in the portal blood more rapidly and more uniformly after infusion of PEP then after infusion of AAL, with the notable exception of methionine for which the opposite was true. These differences were lowered when a carbohydrate (maltose dextrin) was present in the solution, but nevertheless remained significant for the first hour after the infusion. The long‐term (8‐hour) uptake of free amino acids into the liver and the peripheral tissues differed in profile according to the nature of the duodenal infusion. Peripheral uptake was appreciably less well balanced after infusion of free amino acids (deficiency of threonine and phenylalanine) than after infusion of small peptides (deficiency of methionine). Accordingly, in the rat, under conditions of discontinuous enterai nutrition the mixture of small peptides was of greater nutritive value than the mixture of free amino acids. It thus appears that the absorption kinetics which results in important variations in the temporal distribution of free amino acids in the tissues may be at the origin of transitory imbalances in tissue amino acid uptake, and as a result of a lower nutritive value.     

Effect of arginine on the activity of proteolytic enzymes in the rat brain and liver

The influence of arginine on autolysis and proteolysis was studied. Arginine at the concentration of 0.5 and 1.0 microM/ml was added to the incubation mixture. Proteolytic processes were studied in the acid, neutral and alkaline media (pH 4.5; 7.4; 8.5). Autolysis was determined by incubation of the brain and liver homogenates and proteolysis by the use of bovine serum albumin as a substrate. Autolytic and proteolytic activities were calculated as an increase of Folin positive compounds or amino nitrogen in the samples. It was established that the influence in vitro of arginine on the proteolytic processes depended on pH, type of the peptide-hydrolases, to a lesser extent, on the arginine concentration and did not depend on the tissue type. Arginine displayed its regulative action in the brain and liver by the same way. The addition of arginine had an effect on autolysis and proteolysis in the neutral and alkaline media. Determination of autolytic and proteolytic activities by Folin positive compounds has shown that arginine addition into the samples decreased autolysis and proteolysis. At the same time determination of autolysis and proteolysis by amino nitrogen in the presence of arginine has shown that autolytic and proteolytic activities increased.     

Amino acid makeup of preparations from baker's yeast autolysates

Yeast autolysis and hydrolysate composition were studied with respect to the autolysis of baker's pressed yeast. A method of isolating a mixture of amino acids and lower peptides from autolysates was developed, using ion-exchange resins. The above compounds reached maximum accumulation by the 15-20th hour of autolysis. A mixture of amino acids applicable to nutrition, including dietotherapy, was prepared.     

Effect of glutathione on the proteolytic degradation of tissue proteins in young and old rats

The proteolysis rate of the total liver, brain and testicle homogenates from young and old rats was studied by proteolytic enzymes. The level of autolytic destruction of brain and liver proteins decreases with aging. The total liver, brain and testicle proteins of young animals are splitted by pronase faster than the proteins of the old ones. Addition of reduced glutathione to the reaction mixture causes an increase in the rate of liver and brain proteins splitting by pronase in old rats up to the level determined for the young animals. At the same time the effect of glutathione on the testicle tissue of old animals was not observed.     

Fasciola hepatica: A proteolytic digestive enzyme

A proteolytic enzyme in the gut exudate of the common liver fluke has been purified. The enzyme is specific for globin with a pH optimum of 3.9–4.0 and breaks the protein down to peptides and a small percentage of free amino acids. Collagenase activity at pH 7.5 copurifies with the main globinolytic enzyme. The enzyme has a molecular weight of 12,000 and does not appear to be antigenic in fluke-infected animals.     

Effect of arginine and its analogs on the activity of lysosomal and nonlysosomal peptide hydrolases in rat tissues

The autolysis intensity and proteolysis activity at pH 4,5, 7,4, 8,5 and lysosomal and nonlysosomal peptide hydrolase activity have been studied in brain and liver tissues of rats. L-arginine has been found to increase the peptide hydrolase activity in neutral and alkaline media in case of autolysis and proteolysis estimation according to the amino nitrogen increase. When the peptide hydrolase activity is estimated according to the increase of folin-positive components its decrease under the action of arginine in neutral and alkaline media has been revealed. Arginine doesn't change the lysosomal peptide hydrolase activity. In both tissues under the influence of arginine the nonlysosomal peptide hydrolase activity defined by amino nitrogen increases, estimated by the folin-positive components--decreases. Arginine shows the specific influence on the nonlysosomal peptide hydrolase activity. The L-arginine analogues (D-arginine, guanidine) and products of the arginase reaction (ornithine and urea) don't exert such an effect on the nonlysosomal proteolysis.     

Intensity of peroxidation processes and activity of antioxidant enzymes in rat tissues at high chromium level in the diet

The data on the influence of chromium in different tissues of rats at its consumption with mixed fodder in the form of CrCl3 x 6H2O on the intensity of peroxidation processes and activity of antioxidant enzymes are presented. The degree of high chromium content in the studied tissues of rats at its addition to mixed fodder in the amount of 200 microg/kg during 30 days was established. Chromium content in the rat tissues decreased in the order: the spleen, heart, kidneys, lungs, brain, liver, skeletal muscle. In all tissues of rats fed with mixed fodder with chromium addition, except for skeletal muscles, content of lipid peroxidation products--hydroperoxide and TBARS-products decreased. The content of lipid peroxidation products decreased in the spleen, kidneys, liver and lungs. Also in all organs and tissues of rats the activity of glutathione peroxidase, glutathione reductase and catalase increased at the action of chromium. In the brain and kidneys the level of reduced glutathione increased. Superoxide dismutase activity was significantly higher not only in the heart and skeletal muscles of animals and is probably equal in the lungs and liver, and in other organs--the brain, kidneys and spleen in animals of the studied group the enzyme activity was lower as compared to animals of the control group. Obtained results demonstrate the regulatory influence of chromium on free radical process in the rat tissues.     

Free amino acids in brain, liver, and skeletal muscle tissue of voles infected with Trypanosoma brucei gambiense.

The concentrations of several acidic and neutral amino acids of brain, liver, and skeletal muscle were determined in field voles, Microtus montanus, and compared to values obtained from voles harboring a chronic infection of Trypanosoma brucei gambiense. All of the amino acids examined were found at comparable levels in brain tissue from both groups of animals with the exception of tyrosine, which was reduced by approximately 45% in the infected voles. Similarly, the only difference noted in liver tissue was 32% decrease of free tyrosine in the infected animals. With respect to muscle tissue, in addition to a 45% reduction of free tyrosine in the infected voles, decreases of a smaller magnitude were also noted for threonine, glutamate, and valine. The relatively specific alteration of free tyrosine concentrations in the investigated tissues of trypanosome-infected animals suggests an alteration in host metabolism of this amino acid and/or parasite utilization.     

DNA-protein cross-links in nuclei and mitochondria of tissue cells from rats of various age exposed to gamma-radiation

The formation and repair of DNA-protein cross-links (DPC) in the mitochondria and nuclei from the brain and spleen of 2- and 29-month rats after their exposure to ionizing radiation were studied. The background level of DPC in brain and spleen mitochondria of old rats was shown to be about two times as high as in young rats. In the nuclei from the brain of old rats the background amount of DPC was also increased, unlike the nuclei of spleen of the same rats. At the doses 5 and 10 Gy (137Cs), the amount of DPC produced in the mitochondria and nuclei of brain and spleen of 29-month rats was 1.8-2.5 times greater than in the nuclei of the same tissues of young animals. At the same time, in the mitochondria of brain and spleen from irradiated rats the amount of DPC was by 30-80% higher than in the nuclei of the same tissues. Analysis of changes in DPC content during the post-radiation period showed that 5 h after irradiation of rats with a dose of 10 Gy, the level of these lesions in the nuclei of brain and spleen of young rats decreased by 40 and 65%, respectively, whereas the amount of these lesions in the mitochondria did not decrease. In this post-radiation period in nuclei of brain and spleen of old rats the amount of DPC decreased by 20-40%, respectively. However, the data on DPC obtained for the mitochondria of brain and spleen from both young and old rats showed that the amount of these lesions did not decrease during the 5 h post-radiation period. These results enable the suggestion that mitochondria do not possess a system of DPC repair. To summarize, ionizing radiation initiates in the nuclei of brain and spleen of old rats more DPC and their repair proceeds slower than in the nuclei of the same tissues of young animals. In the mitochondria of gamma-radiation exposed old rats more DPC are also produced than in young rats but no repair of DPC is observed in both old and young animals within the 5 h post-radiation period.     

Isoaccepting transfer ribonucleic acids in liver and brain of young and old BC3F1 mice

Transfer RNAs from liver and brain of young and old BC3F₁ mice were compared in regard to extent of aminoacylation and cochromatographic profiles of isoaccepting tRNA species on reversed-phase columns. Homologous synthetase preparations and optimal aminoacylation conditions were employed, having been determined for each amino acid and found to be the same for those from old and young mice. Small differences were found between tRNAs from young and old mice in the extent of acceptance for arginine and tyrosine in the liver and for aspartic acid in the brain. There were no differences observed between preparations from young and old mice in any of the cochromatographic profiles for the amino acids examined in this study, which included arginyl-, aspartyl-, glutamyl-, histidyl-, leucyl-, lysyl-, phenylalanyl-, seryl-, and tyrosyl-tRNAs from liver and arginyl-, aspartyl-, histidyl-, leucyl-, lysyl-, and seryl-tRNAs from brain. Comparisons of tRNA preparations from fetal and neonatal liver with those from adult liver did reveal both qualitative and quantitative differences. These results suggest that the postulated accumulation of errors as a result of age-related alterations in the translational mechanism does not occur in tRNA or aminoacyl-tRNA synthetases of these two tissues.     

Protease A activity and nitrogen fractions released during alcoholic fermentation and autolysis in enological conditions

Determination of protease A activity during alcoholic fermentation of a synthetic must (pH 3.5 at 25°C) and during autolysis showed that a sixfold induction of protease A activity occurred after sugar exhaustion, well before 100% cell death occurred. A decrease in protease A activity was observed when yeast cell autolysis started. Extracellular protease A activity was detected late in the autolysis process, which suggests that protease A is not easily released. Evolution of amino acids and peptides was determined during alcoholic fermentation and during autolysis. Amino acids were released in early stationary phase. These amino acids were subsequently assimilated during the fermentation. The same pattern was observed for peptides; this has never been reported previously. During autolysis, the concentration of amino acids and peptides increased to reach a maximum of 20 and 40 mg N l⁻¹, respectively. This study supports the idea that although protease A activity seemed to be responsible for peptides release, there is no clear correlation among protease A activity, cell death, and autolysis. The amino acid composition of the peptides showed some variations between peptides released during alcoholic fermentation and during autolysis. Depending on aging time on yeast lees, the nature of the peptides present in the medium changed, which could lead to different organoleptic properties. Journal of Industrial Microbiology & Biotechnology (2001) 26, 235–240. Received 02 August 2000/ Accepted in revised form 15 December 2000     

Age features of oxidative processes in rat liver caused by toxic damage from tetrachloromethane]

It has been studied the effect of tetrachlormethane on the activity of the processes of microsomal mitochondrial and free radical oxidation in 3.8-10 and 20-24 month rats. The age peculiarities of the investigated processes have been ascertained. The introduction of CCl4 caused: the most increase of the level of free radical oxidation products in young animals. The activity of oxidative processes in microsomes were minimum in this group of animals. In old rats the contents of intermediate products of FRO increased in the least degree and end products--the same as young animals. The oxidative processes in mitochondria were decreased in the most degree in old rats. It has been concluded that the activation of free radical reactions by active metabolites of CCl4 plays the main role in progress of pathological processes in young animals and the covalent connection of low active radicals with proteins of membranes and enzymes in old rats.     

Sensitivity to in vitro lipid peroxidation in liver and brain of aged rats.

Lipid peroxidation in rat liver and brain has been studied to see if it increases with old age. No significant differences in the level of endogenous, nonstimulated lipid peroxidation (TBA-RS) is found between 9 month-old (mature adults) and 28 month-old animals in liver or cerebral cortex. Liver homogenates subjected in vitro to an oxidative stress (ascorbate-Fe++), show a clearly slower peroxidation rate in old than in young animals. On the other hand, the in vitro peroxidation rate of cerebral homogenates was similar in young and old animals. The in vitro peroxidation rate was much higher in brain than in liver tissue. These results do not support the view that old rats liver and brain are more susceptible to free radical oxidative damage than those of young ones.     

Coomassie brilliant blue G-250 dye-binding technique for determination of autolytic protein breakdown in Euglena gracilis and comparison to other methods of autolysis measurement

The Coomassie brilliant blue G-250 dye-binding technique of M. M. Bradford (1976, Anal. Biochem. 72, 248-254) for protein quantification has been used to measure autolytic protein breakdown in cell-free extracts of Euglena gracilis. Specific autolysis rates were calculated from the difference between initial and actual absorbances at different incubation times of Coomassie brilliant blue-stained protein. They were found to depend linearly on time and initial protein concentration. Calibration against another method of protein determination is necessary due to different color yields with various protein mixtures. The high sensitivity and reproducibility of this method permit determination of specific autolysis rates below 0.1% mg-1 h-1 over a pH range between 3 and 8, without protein precipitation or pH adjustment, and in the presence of high amounts of amino acids and/or small peptides. Results obtained by this method are comparable to those of other autolysis measurements and to proteolytic activity determination by azocaseinolysis. Proteolytic autolysis has been observed in both the soluble and the particulate fractions of E. gracilis cell-free extracts, but displays different pH optima and specific activities in these fractions, as is also the case for azocaseinolysis. The method described is easy to perform, inexpensive, time saving, and should be applicable to other biological systems as well.     

Brain protein synthesis rates are not sensitive to elevated GABA,taurine, or glycine

The effects of elevated levels of GABA, glycine, or taurine on the rate of protein synthesis in plasma, brain, liver, and muscle of adult mice were measured in in vivo experiments after a flooding dose of labeled valine. Elevation of these amino acids caused hypothermia; keeping the animals in an incubator maintained physiological body temperature. The increase in GABA or glycine did not affect the rate of protein synthesis in these tissues to a significant degree. The increase in taurine levels caused inhibition of valine incorporation in plasma, liver, and muscle, while brain protein synthesis was unaffected. When glycine was increased in brain, the uptake of labeled free valine in the brain was greater.     

Genetics of the proteolytic system of lactic acid bacteria

Abstract The proteolytic system of lactic acid bacteria is of eminent importance for the rapid growth of these organisms in protein-rich media. The combined action of proteinases and peptidases provides the cell with small peptides and essential amino acids. The amino acids and peptides thus liberated have to be translocated across the cytoplasmic membrane. To that purpose, the cell contains specific transport proteins. The internalized peptides are further degraded to amino acids by intracellular peptidases. The world-wide economic importance of the lactic acid bacteria and their proteolytic system has led to an intensive research effort in this area and a considerable amount of biochemical data has been collected during the last two decades. Since the development of systems to genetically manipulate lactic acid bacteria, data on the genetics of enzymes and processes involved in proteolysis are rapidly being generated. In this review an overview of the latest genetic data on the proteolytic system of lactic acid bacteria will be presented. As most of the work in this field has been done with lactococi, the emphasis will, inevitably, be on this group of organisms. Where possible, links will be made with other species of lactic acid bacteria.     

Genetics of the proteolytic system of lactic acid bacteria

The proteolytic system of lactic acid bacteria is of eminent importance for the rapid growth of these organisms in protein-rich media. The combined action of proteinases and peptidases provides the cell with small peptides and essential amino acids. The amino acids and peptides thus liberated have to be translocated across the cytoplasmic membrane. To that purpose, the cell contains specific transport proteins. The internalized peptides are further degraded to amino acids by intracellular peptidases. The world-wide economic importance of the lactic acid bacteria and their proteolytic system has led to an intensive research effort in this area and a considerable amount of biochemical data has been collected during the last two decades. Since the development of systems to genetically manipulate lactic acid bacteria, data on the genetics of enzymes and processes involved in proteolysis are rapidly being generated. In this review an overview of the latest genetic data on the proteolytic system of lactic acid bacteria will be presented. As most of the work in this field has been done with lactococci, the emphasis will, inevitably, be on this group of organisms. Where possible, links will be made with other species of lactic acid bacteria.     

Yeast adapted to wine: nitrogen compounds released during induced autolysis in a model wine

As important as the blend of base wines before bottling, one of the most important steps in the champagne-making process is the long ageing on lees. Two yeast strains of Saccharomyces cerevisiae MC001 and MC002, used in champagne wine production, were allowed to autolyse. After 8 days of autolysis, active dry yeasts adapted to wine released 1.7- to 1.8-fold more nitrogen compounds than nonadapted active dry yeast. The nitrogen content (total, proteins, peptides and amino) present in autolysates was measured for yeasts adapted to wine. The composition of free amino acids and amino acids constituting peptides showed no difference between the two strains of yeast used. Studies of intracellular proteolytic activity and release of peptides showed no correlation between these two phenomena. These results indicate that yeasts adapted to wine give results similar to those that occur in wine during ageing. Journal of Industrial Microbiology & Biotechnology (2002) 29, 134–139 doi: 10.1038/sj.jim.7000291 Received 19 December 2001/ Accepted in revised form 14 June 2002     

Dynamics of free amino acids in rat brain tissue during hypothermia

A comparative study is conducted for the effect of one-, three- and six-hour artificial deep (20-19 degrees C) hypothermia on the content of free amino acids in the blood serum, tissue, nuclei and mitochondria of the rat brain. It is found out that the content is the highest in the blood serum after a three-hour cooling. In the brain tissue the amount of amino acids lowers, especially under conditions of a six-hour hypothermia. In nuclei a three-hour effect of hypothermia decreases sharply the content of free amino acids and the six-hour one increases the amount of most of them. Under hypothermia the content of nearly all amino acids in the brain mitochondria is higher than in the intact animals.     

Age-related changes in the activity of free-radical processes in rat tissues and blood serum]

Activity of Cu,Zn-superoxide dismutase (SOD) in old rats' brain was found to be decreased by 46.8% as compared to young animals. The brain concentration of Schiff bases (SB) was decreased by 13.6% in old rats, whereas concentration of diene conjugates (DC), protein peroxidation (PP), and total antioxidative activity (TAA) was the same in old as well as in young rats. The liver level of the DC and TAA was also the same. The serum level of the PP, SB, and DC was increased whereas the activity of the SOD and TAA was decreased in old rats. The findings suggest occurrence of considerable age-related changes in free radical processes as well as the organ specifics of these changes in rats.