Quantitative analysis of the relationship between structure and antioxidant activity of tripeptides

Peptides from enzymatic hydrolysates of food proteins exhibit significant antioxidant activity. Several studies have attempted to determine the factors contributing to the antioxidant activity of peptides; however, the physicochemical properties and factors essential for the antioxidant activity of peptides are still unclear. In this study, in order to clarify the factors important for peptide antioxidant activity based on the properties of component amino acids, 55 tripeptides were synthesized from 20 natural amino acids and their antioxidant activity was measured using the Trolox equivalent antioxidant capacity (TEAC) assay system. The tripeptides were divided into two data sets: a training set comprising 50 compounds and a validated set comprising five compounds. The structure‐activity relationship of the training set was then analyzed using classical quantitative structure‐activity relationship (QSAR) analysis. The study findings demonstrate that the presence of a cysteine residue at any position, an aromatic amino acid at the C‐terminus, higher hydrophobicity of the N‐terminal residue, and smaller HOMO‐LUMO energy gap of the middle residue can significantly enhance the antioxidant activity. The activities of the five validated compounds were predicted using the constructed QSAR model, and a good correlation between measured and predicted activities was observed. The information obtained from the QSAR model could be useful for effective production of antioxidant peptides from food proteins such as egg white proteins.     

Chemical composition and antioxidant activities of Broussonetia papyrifera fruits

Fruits of Broussonetia papyrifera from South China were analyzed for their total chemical composition, and antioxidant activities in ethanol and aqueous extracts. In the fruit of this plant, the crude protein, crude fat and carbohydrates was 7.08%, 3.72% and 64.73% of dry weight, respectively. The crude protein, crude fat and carbohydrates were 15.71%, 20.51% and 36.09% of dry weight, respectively. Fatty acid and amino acid composition of the fruit were analyzed. Unsaturated fatty acid concentration was 70.6% of the total fatty acids. The percentage of the essential amino acids (EAAs) was 40.60% of the total amino acids. Furthermore, B. papyrifera fruit are rich in many mineral elements and vitamins. Total phenolic content was assessed using the Folin-Ciocalteau assay, whereas antioxidant activities were assessed by measuring the ability of the two extracts to scavenge DPPH radicals, inhibit peroxidation, and chelate ferric ions. Their reducing power was also assessed. Results indicated that the aqueous extract of B. papyrifera was a more potent reducing agent and radical-scavenger than the ethanol extract. GC-MS analysis of the ethanol extract showed the presence of some acid-containing compounds. The changes in total phenolic content and antioxidant capacity in B. papyrifera from four different regions grown under normal conditions were assessed. The antioxidant activity of different extracts was positively associated with their total phenolic content. These results suggest that the fruit of B. papyrifera could be used in dietary supplement preparations, or as a food additive, for nutritional gain, or to prevent oxidation in food products.     

Antioxidant Effect of Peptide in Combination with Sugar on Autoxidation of Edible Oils

The antioxidant effect of various combinations of peptide and sugar was investigated by an oven-storage test using lard as substrate. High antioxidant activity was resulted from combining a peptides with branched-chain amino acids and xylose. For this effect, the presence of a branched-chain amino acid was more favorable at the N-terminal position of the peptide than at the C-terminal position. A synergistic effect was observable with xylose at a molar ratio of xylose-peptide of 0.05. The leucylglycine-xylose composition was also effective for preventing oxidation in selected vegetable oils.     

Amino acids and plasma antioxidant capacity

Summary Amino acids antioxidant capacity has been investigated and compared with the chain-breaking antioxidant activity of known compounds as ascorbic acid and Trolox. Basic and acidic amino acids and most of neutral ones showed no antioxidant capacity. On the contrary, tryptophan, tyrosine, cysteine and homocysteine showed antioxidant ability at concentrations which are within the usually reported physiological ranges.These findings are discussed in connection with the antioxidant capacity ascribed to plasma proteins, as human serum albumin.     

Purification and characterization of high antioxidant peptides from duck egg white protein hydrolysates

The hydrolysate from duck egg white protein (DEWP) prepared by “SEEP–Alcalase” at degree of hydrolysis (DH) value of 21% (namely HSA₂₁) exhibited high antioxidant capacity in different oxidation systems. A consecutive chromatographic method was then developed for separation and purification of HSA₂₁, including ion-exchange chromatography, macroporous adsorption resin (MAR) and gel filter chromatography. The final peptides “P_21-3–75-B” were obtained with significantly enhanced antioxidant activity (p < 0.05). It was further confirmed that the product mainly consisted of five oligopeptides (Mr: 202.1, 294.1, 382.1, 426.3, and 514.4 Da). Furthermore, the antioxidant activity of P_21-3–75-B kept stable after in vitro digestive simulation. Antioxidant capacity of the purified peptides was closely related to the molecular mass, hydrophobic amino acid residues, acidic amino acid and some antioxidant amino acids. This research provided a valuable route for producing new natural-source peptides with strong antioxidant capacity and high nutritious value for our daily intake.     

Molecular mechanism of recombinant liver fatty acid binding protein's antioxidant activity

Hepatocytes expressing liver fatty acid binding protein (L-FABP) are known to be more resistant to oxidative stress than those devoid of this protein. The mechanism for the observed antioxidant activity is not known. We examined the antioxidant mechanism of a recombinant rat L-FABP in the presence of a hydrophilic (AAPH) or lipophilic (AMVN) free radical generator. Recombinant L-FABP amino acid sequence and its amino acid oxidative products following oxidation were identified by MALDI quadrupole time-of-flight MS after being digested by endoproteinase Glu-C. L-FABP was observed to have better antioxidative activity when free radicals were generated by the hydrophilic generator than by the lipophilic generator. Oxidative modification of L-FABP included up to five methionine oxidative peptide products with a total of ∼80 Da mass shift compared with native L-FABP. Protection against lipid peroxidation of L-FABP after binding with palmitate or α-bromo-palmitate by the AAPH or AMVN free radical generators indicated that ligand binding can partially block antioxidant activity. We conclude that the mechanism of L-FABP''s antioxidant activity is through inactivation of the free radicals by L-FABP''s methionine and cysteine amino acids. Moreover, exposure of the L-FABP binding site further promotes its antioxidant activity. In this manner, L-FABP serves as a hepatocellular antioxidant.     

苹婆种子营养及抗氧化活性

介绍了一种原产华南、种子可食的木本植物——苹婆的生物学特性,并以广西苹婆（Sterculia nobilisSmith）种子为材料,对其营养成分进行了测定。通过测定其多酚提取物的还原力和金属螯合力,以及对1,1-二苯基-2-三硝基苯肼（DPHH）自由基、羟自由基和超氧阴离子自由基的清除能力,探讨了苹婆种子的抗氧化活性。结果显示：苹婆种子营养丰富,含有18种氨基酸,富含酚类物质。其中,淀粉含量60.42 g/100 g FW、蛋白质20.32 g/100 g FW、脂肪2.18 g/100 g FW、氨基酸2.36 g/100 g FW、铁136.86 mg/g FW、维生素C 7225μg/100 g FW;总酚含量为401.84μg/mL没食子酸。苹婆种子多酚提取物有较强的还原力,金属螯合力,以及DPPH自由基、羟自由基和超氧阴离子自由基清除能力,在0～50μg/mL浓度范围,苹婆抗氧化能力与抗坏血酸或乙二胺四乙酸（EDTA）相当。苹婆种子营养全面,具有较强的抗氧化能力,苹婆是很有潜力的功能食品来源植物。     

Extraction of protein and amino acids from deoiled rice bran by subcritical water hydrolysis

This study investigated the production of value-added protein and amino acids from deoiled rice bran by hydrolysis in subcritical water (SW) in the temperature range between 100 and 220 degrees C for 0-30 min. The results suggested that SW could effectively be used to hydrolyze deoiled rice bran to produce useful protein and amino acids. The amount of protein and amino acids produced are higher than those obtained by conventional alkali hydrolysis. The yields generally increased with increased temperature and hydrolysis time. However, thermal degradation of the product was observed when hydrolysis was carried out at higher temperature for extended period of time. The highest yield of protein and amino acids were 219 +/- 26 and 8.0 +/- 1.6 mg/g of dry bran, and were obtained at 200 degrees C at hydrolysis time of 30 min. Moreover, the product obtained at 200 degrees C after 30 min of hydrolysis exhibited high antioxidant activity and was shown to be suitable for use as culture medium for yeast growth.     

Dual effects of caffeoyl-amino acidyl-hydroxamic acid as an antioxidant and depigmenting agent

Anti-aging and depigmentation have both been an important subject of study for skin disease and the cosmetic industry. Caffeic acid (CA) has shown synergistically enhanced antioxidant activity when conjugated with amino acids. Hydroxamic acid (NHOH) is a well-known metal chelator, potentially having both tyrosinase inhibitory activity and free radical scavenging activity. We prepared caffeoyl-amino acidyl-hydroxamic acid (CA-Xaa-NHOH) and found that caffeoyl-prolyl-hydroxamic acid (CA-Pro-NHOH) contained excellent antioxidant activity and tyrosinase inhibitory activity by various bioassay systems. Also, CA-Pro-NHOH showed mild melanogenesis inhibitory activity in Mel-Ab cells.     

Peptides with antioxidant properties identified from casein,whey, and egg albumin hydrolysates generated by two novel fungal proteases

Abstract

There are many diseases linked to oxidative stress, including cancer. Importantly, endogenous antioxidants are insufficient to protect against this process. Peptides derived from food proteins produced by hydrolysis have been investigated as exogenous antioxidants. The present study aimed to identify novel peptides with antioxidant potential produced from egg and milk proteins hydrolysis with two new fungal proteases isolated from Eupenicillium javanicum and Myceliophthora thermophila. The degree of hydrolysis at several time points was calculated and correlated to DPPH scavenging and metal chelating assays, all hydrolysates presented antioxidant activity. Casein hydrolyzed by the M. thermophila protease showed the best antioxidant activity. The identified sequences showed that the proportions of amino acids that influence antioxidant activity support the antioxidant assay. Our data reveal the conditions necessary for the successful generation of antioxidant peptides using two novel fungal proteases. This opens a potential new avenue for the design and manufacture of antioxidant molecules.     

TRANSAMINATION OF AMINO ACIDS IN HOMOGENATES OF RAT BRAIN

Abstract— The aminotransferase activity of homogenates of brains from adult and neonatal rats has been investigated. Aminotransferase activity was demonstrated wtih 15 of 22 amino acids incubated with seven keto acids. The basic amino acids exhibited little or no activity.

• 1 The greatest activity was obtained when glutamate or aspartate was incubated with α-ketoglutarate or oxaloacetate. Significant activity was also observed when the neutral aliphatic and aromatic amino acids were incubated with these two keto acids.
• 2 Activity with pyruvate was obtained principally upon incubation with glutamate and alanine. Most of the other amino acids that underwent transamination with α-ketoglutarate also did so with pyruvate, although at a lower rate.
• 3 When phenylpyruvate was added to the medium, glutamate, phenylalanine and tyrosine transaminated most actively.
• 4 Incubations with 11 amino acids and glyoxylic acid demonstrated aminotransferase activity, with glutamate and ornithine being the most active substrates.
• 5 α-Ketoisocaproate and α-ketoisovalerate accepted amino groups primarily from the branched-chain amino acids. Except for glutamate, activity with other amino acids was low or not detectable.
• 6 A comparison of aminotransferase activity in the newborn brain with that in the adult brain showed that the greatest change in activity occurred for glutamate with pyruvate or for alanine with α-ketoglutarate, these activities increasing about 10-fold from birth to adulthood; during this time activities with most other amino acids increased two- to threefold. Amino transfers from the branched-chain amino acids showed no increase with maturation, and some reactions, such as that with methionine and a number of keto acids, decreased from birth to adulthood.
• 7 Our results correspond in general to previous studies of aminotransferase activity in brain and in liver. However, our study also indicates a possible second aminotransferase acting on the branched-chain amino acids, the presence of aminotransferase activity for methionine and asparagine, and relatively high aminotransferase activity for glutamine or ornithine when incubated with glyoxylic acid rather than other keto acids. Moreover, phenylpyruvate and glyoxylate are active in amino transfers and may serve as substrates for a number of aminotransferases.

     

Influence of amino acids on the activity of cellulolytic enzymes obtained from spent medium of Fusarium cultures and on the "Cellulase S" Novo.

Comparative studies on the influence of 4 amino acids (cysteine, cystine, methionine and alanine) on the activity of enzymatic preparation were carried out. The action of the amino acids was shown to depend on pH, incubation time and the temperature of incubation. Attempts were made to find a correlation between the amino acids introduced and redox potential (Eh), pH and the activity of the cellulolytic enzymes. It was found that the addition of some amino acids to the reaction mixtures at different pH values affected the value of Eh -- which enhanced the cellulase activity.     

Synthesis of cinnamoyl and hydroxycinnamoyl amino acid conjugates and evaluation of their antioxidant activity.

Fifteen amides of cinnamic, ferulic and sinapic acids with natural and unnatural C-protected amino acids have been synthesized. The amides (E)-N-(feruloyl)-L-tyrosine methyl ester (10), (E)-N-(feruloyl)-L-phenylalanine t-butyl ester (11), (E)-N-(sinapoyl)-L-tyrosine methyl ester (13) and (E)-N-(sinapoyl)-L-phenylalanine t-butyl ester (15) with a free carboxyl group of amino acids have been found in nature. The rest of the compounds are unknown. The hydroxycinnamoyl amino acid conjugates have been studied for their antioxidant activity (AOA) in bulk phase lipid autoxidation. The highest AOA has been found for the compounds 11 and 15, which contain the same phenylalanine moiety.     

ALTERATION OF GABA SYSTEM AND PURKINJE CELLS IN RAT CEREBELLUM BY THE CONVULSANT 3-MERCAPTOPROPIONIC ACID

Abstract— The effect of the convulsant, 3-mercaptopropionic acid (MP) on the content of free amino acids and on the activity of some enzymes related to their metabolism was studied in the rat cerebellum. A decrease in the activity of glutamate decarboxylase (EC 4.1.1.15) and in the level of GABA was found; at the same time, the activity of GABA-aminotransferase (EC 2.6.1.19) was increased. These changes coincided with a profound alteration of the morphology of the Purkinje cells which was related to the dose of MP. These findings, plus some changes in the content of other free amino acids and the activities of related enzymes, suggest that 3-mercaptopropionic acid induces in the cerebellum an imbalance among the amino acids involved in the excitation-inhibition mechanisms.     

Regulation of glutamate dehydrogenase activity by amino acids in maize seedlings

Root or secondary leaf segments from maize ( Zea mays L. cv. Ganga safed-2) seedlings were incubated with 9-amino acids and two amides separately, each at 5 m M for 24 h, to study their effects on glutamate dehydrogenase (GDH) activity. Most of the compounds tested inhibited the specific activity of NADH-GDH and increased that of NAD⁺-GDH in the roots in the presence as well as in the absence of ammonium. In the leaves, such effects were recorded only with a few amino acids. Total soluble protein in the root and leaf tissues increased with the supply of most of the amino compounds. The effect of glutamate on enzyme activity and protein was concentration dependent in both tissues. When the enzyme extracts from root or leaf tissues were incubated with some of the amino acids, NADH-GDH declined while NAD⁺-GDH increased in most cases. The inhibition of NADH-GDH increased with increasing concentration of cysteine from 1 to 5 m M . The experiments demonstrate that most of the amino acids regulated GDH activity, possibly through some physicochemical modulation of the enzyme molecule.     

Mutagenic activity of amino acid pyrolyzates in Salmonella typhimurium TA 98.

Pyrolyzates of 25 amino acids and 5 indole derivatives were tested for mutagenicity in the histidine-requiring mutant Salmonella typhimurium TA 98. Significant mutagenic activity was detected with pyrolyzates of most of the amino acids. These pyrolyzates required a liver microsomal fraction, as representative of mammalian metabolism, to be detected as mutagens. Among the pyrolyzates tested, the highest mutagenic activity was observed with that of L-tryptophan. As little as 10 microgram of the pyrolyzate of L-tryptophan had detectable mutagenic activity toward TA 98. The optimal pyrolysis temperatures for the formation of mutagenic products were shown to be 500 degrees C for L-tryptophan and 600 degrees C for the other amino acids. The results from pyrolyses of some indole derivatives suggest that an amino group at the alpha-position to the carboxyl group of L-tryptophan plays an important role in the formation of mutagens.     

Synthesis and Antioxidant Evaluation of O-Methylated Emodacidamides: Starting from Parietin,a Secondary Metabolite of Lichen Xanthoria parietina

Polyhydroxy-anthraquinones bearing amino acids are found rather seldom in nature. Emodacidamides, isolated from a marine-derived fungus, Penicillium sp. SCSIO sof101 by Luo et al. (2017) are the first natural example of amino acid conjugated anthraquinone. In this study, O-methylated emodacidamides and emodinic acid-anilides were synthesized starting from parietin, extracted from the lichen Xanthoria parietina (L.) Th. Fr. The structural elucidations of prepared compounds were confirmed by 1D and 2D NMR analyses including HSQC and HMBC techniques. In addition, all newly synthesized compounds were evaluated for the antioxidant activities with free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging. The synthesized compounds showed low to moderate antioxidant and DPPH scavenging activities. The antioxidant activities were supported within quantum chemical calculations using the DFT−B3LYP/6-311++G(d,p) level of theory. It is observed that the antioxidant activity of emodacidamides mostly depends on the phenolic groups on anthraquinone ring. The phenolic groups on other substituents help to improve antioxidant activity and also the position of hydroxy group is a decisive factor for antioxidant ability.     

饲料中添加杜仲叶粉对黄河鲤体成分、肌肉氨基酸组成和生理指标的影响

试验以黄河鲤(Cyprinus carpio)为研究对象,以饲料中杜仲(Eucommia ulmoides)叶粉0添加组为对照组,2%、4%、6%和8%添加组为实验组,每组3个平行,对黄河鲤[体重:(505.13±1.37) g]进行55d的投喂试验,旨在探讨杜仲叶粉在黄河鲤饲料中的应用效果。结果表明:(1)黄河鲤背肌脂肪含量随饲料中杜仲叶粉添加量升高显著下降,粗蛋白含量显著上升(P<0.05)。除6%添加组外,鱼体粗灰分、粗蛋白和粗脂肪鲜重含量随杜仲叶粉添加量升高呈上升趋势(P<0.05),鱼体鲜重水分含量呈显著下降趋势(P<0.05);(2)在黄河鲤肌肉中检出16种氨基酸,杜仲叶粉添加显著影响肌肉中苏氨酸、丝氨酸和组氨酸含量(P<0.05)。酸味氨基酸总量与总氨基酸比值在2%添加组显著高于其他处理组,药效氨基酸总量与总氨基酸比值则在2%添加组显著低于其他处理组(P<0.05);(3)黄河鲤血浆和肝脏中GSH-PX、MDA、AKP和ACP活性随饲料中杜仲叶粉添加量增加整体呈先升高后降低趋势,血浆和肝脏中SOD活性呈显著上升趋势(P<0.05)。血浆...     

Transamination of L-cystathionine and related compounds by a bovine liver enzyme. Possible identification with glutamine transaminase

A transaminase which catalyses the monodeamination of L-cystathionine was purified 1100-fold with a yield of 15% from bovine liver. The monoketoderivative of cystathionine spontaneously produces the cyclic ketimine. Other sulfur-containing amino acids related to cystathionine such as cystine, lanthionine and aminoethylcysteine were also substrates for the enzyme. The relative molecular mass of the enzyme was determined to be 94 000 with a probable dimeric structure formed of identical subunits. The isoelectric point of the enzyme was at pH 5.0 and the maximal enzymatic activity was found at pH 9.0--9.2. Kinetic parameters for cystathionine and for the other sulfur amino acids as well as for some alpha-keto acids were also determined. Among the natural amino acids tested, glutamine, methionine and histidine were the best amino donors. The enzyme exhibited maximal activity toward phenylpyruvate and alpha-keto-gamma-methiolbutyrate as amino acceptors. The broad specificity of the enzyme leads us to infer that the cystathionine transaminase is very similar or identical to glutamine transaminase.     

The use of some nanoemulsions based on aqueous propolis and lycopene extract in the skin's protective mechanisms against UVA radiation

Background  

The use of natural products based on aqueous extract of propolis and lycopene in the skin's protective mechanisms against UVA radiation was evaluated by means of experimental acute inflammation on rat paw edema. The aim of the present study was to evaluate the harmlessness of propolis - lycopene system through evaluation of skin level changes and anti-inflammatory action. The regenerative and protective effect of the aqueous propolis and lycopene extract is based on its richness in biologically active substances such as: tocopherols, flavonoids, amino acids, polyunsaturated fatty acids, the chlorophyll pigment, all substances with strong antioxidant activity, that modify the oxidative stress, mainly by reducing the prooxidant processes and enhancing the antioxidant ones. These substances participate in the synthesis of prostaglandins and phospholipids components of cell membrane thus enhancing skin protection mechanisms.