Disulphide Bond Content Research Articles

Pleurotus geesteranus mycelium proteins: physicochemical and functional properties

SummaryIn the present work, the physicochemical and functional properties, as well as the digestion behaviour of Pleurotus geesteranus mycelium protein isolates (PMPI), were investigated. SDS‐PAGE results found that the molecular weight of PMPI was mainly concentrated in >100 kDa and <25 kDa and a total of 365 proteins were detected with proteome analysis. The contents of secondary structures in PMPI were as follows: β‐sheet (27.15%) > α‐helix (23.23%) > random coil (21.92%) > β‐turn (17.21%) > β‐antiparallel (10.48%). The total sulphydryl, free sulphydryl and disulphide bond content of PMPI were 29.88, 9.77 and 10.05 μmol/g respectively. The denaturation temperature of PMPI was measured at 92.94 °C, with an enthalpy change of 39.76 J/g. However, PMPI showed poor solubility, leading to relatively low foaming properties and emulsion activity. The nitrogen release rate of PMPI was 21.78% after pepsin digestion and 74.60% at the end of trypsin digestion.

Effects of innovative gelation and modified tapioca starches on the physicochemical properties of surimi gel during frozen storage

SummaryThis study presented a comparative evaluation of the effects of 5% tapioca starch, acetylated distarch phosphate and hydroxypropyl distarch phosphate (HPDSP) on the changes in surimi gel quality after the traditional gelation procedure (suwari‐cooking‐freezing) and a novel gelation procedure (suwari‐freezing‐cooking, SFC). Overall, subjected to the SFC procedure, lower hydrophobic interactions, lower total sulphydryl group content, higher disulphide bond content and a more orderly protein conformation was observed in the HPDSP‐surimi gel. These changes resulted in smaller drip loss, stabler breaking force and deformation, and less structural damage during frozen storage. Since the strongest hydrophilicity of HPDSP and the lowest gelatinisation temperature (63.15 °C), when it was reheated and then gelatinized, it interacted more closely with the protein. These findings indicated that subjected to the SFC procedure, the addition of 5% HPDSP effectively decreased the changes in the quality of the surimi gel.

Poultry feather disulphide bond breakdown to enable bio-based polymer production

With oil supplies, needed for plastic production, decreasing dramatically, there is a clear driver for alterative polymers from sustainable resources. Poultry feathers, containing ∼90% keratin, are one source of natural polymer with huge potential for biopolymer production. However, the presence of crosslinks, known as disulphide bonds, hinders processability. This paper reviews techniques to enable breakage of disulphide bonds through use of reduction agents (sodium sulphite and sodium sulphate) and hydrolysis. Samples were analysed using FTIR and DSC to quantify achievable bond breakage, effect on thermal properties and changes in protein concentration. A review on the effect of particle size on disulphide bond breakage was also conducted, along with quantifying the reformation of bonds post-processing. Finally, a bicinchoninic acid (BCA) protein assay was used to quantify changes to soluble protein content, key to predicting if biopolymer formation can occur. The results showed a final disulphide bond breakage of between 48% and 67% was achievable using these techniques. It was also shown that disulphide bond content exhibited up to 60% bond reformation post treatment. These reductions in disulphide bonds increased the thermoplastic nature and apparent protein content. Despite achieving the highest bond breakage percentage, hydrolysis caused degradation of useful proteins, rendering the material unsuitable for biopolymer production. Results suggested that treatment with sodium sulphite (4.3% wt. of feathers) and use of a small particle size (0–100 µm), sufficiently altered the properties of raw feathers to enable feather biopolymer production.

Ethnic hair: Thermoanalytical and spectroscopic differences.

The aim of this study is to characterize and detect the possible differences among the hair of three different ethnicities: African, Asiatic and Caucasian. The differences in water adsorption/desorption behaviour of hairs were studied using a thermogravimetric balance and compared with the analysis of the lipid distribution and order using synchrotron-based Fourier transform infrared microspectroscopy. Besides, the thermal thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses on human hair were executed. Differences in the diffusion coefficients were evidenced. African hair exhibited increased permeability. Caucasian hair displayed a higher water absorption capability with increasing humidity but with a slow diffusion rate. The Asian fibre appeared to be more resistant to hydration changes. The spectroscopic analysis showed notable differences in the cuticle lipids. The African cuticle exhibited more lipids with a lower order bilayer. The outmost layer of Caucasian fibres contained more ordered lipids, and the Asian fibres show a very low level of lipids on the cuticle region. The DSC results indicate no difference in the thermal stability and TG showed higher water content in the Caucasian fibre and a possible lower cysteine disulphide bond content in the African hair matrix. The triple approach demonstrated the permeability differences among the ethnic fibres and their correlation with the properties of their cuticle lipids. These differences could have particular relevance to the hair care cosmetic market.

Disulphide bonds and cross‐linked amino acids may affect amino acid utilization in feather meal fed to rainbow trout (Oncorhynchus mykiss)

A digestibility trial was carried to assess the apparent digestibility coefficient (ADC) of crude protein (CP) and amino acids (AA) in two feather meals (FeM) of different origin (FeM1 and FeM2) and in their enzymatically pre-treated ingredient stream (PTFeM1 and PTFeM2) in rainbow trout. The ADC of CP was 11%–17% higher (p < 0.05) in the PTFeMs than in their FeM counterparts. There was no difference (p > 0.05) of ADC of CP among FeMs and among PTFeMs. The FT-Raman analysis showed a reduction in concentration and conformational stability of disulphide bonds in the PTFeMs when compared to their FeM counterparts. Moreover, important discrepancies in disulphide concentration were observed between FeMs and between PTFeMs. These observations suggest that the ADC of CP in FeM is not only governed by disulphide bond content and other variables should be considered. Higher concentrations of the cross-linked amino acids (CLAA) lanthionine, lysinoalanine and β-aminoalanine were measured in FeM1 and PTFeM1 as compared to FeM2 and PTFeM2 respectively. Previous studies have suggested inverse relationships between CLAAs and the digestibility as well as bioavailability of AAs in feed ingredients. A previous study conducted in our laboratory showed a lower (p < 0.05) bioavailability of arginine in FeM1 and PTFeM1 than in FeM2 and PTFeM2, respectively, in rainbow trout. Our results suggest that (a) the digestibility of AAs in FeM may be affected by disulphide bond content and the presence of CLAAs, and (b) CLAA content may be indicator of bioavailability of AAs in FeM.

Physical, Chemical Properties and Structural Changes of Zaodan Pickled by Vacuum Decompression Technology.

To shorten the production cycle of Zaodan, this study first pickled Zaodan by a novel technology - vacuum decompression technology. Vacuum decompression technology could reduce the pickling time of Zaodan from 20 wk to about 9 wk. The protein content, moisture and pH of the Zaodan egg white gradually decreased with a concomitant increase in salt during the pickling process. The total sulfhydryl group (SH) group content of the egg white proteins was increased to 2.43×10-3 mol/L after being pickled for 30 d, whereas the content of disulphide bonds (SS) was reduced to 23.35×10-3 mol/L. The surface hydrophobicity was lowest after pickling for 30 d. In addition, great changes occurred in the secondary structure of the egg white proteins after pickling for 20 d. The disappearance of ovomucin was noticeable based on sodium dodecyl sulfate–polyacrylamide gel electrophoresis analysis.

Combined effect of squid ink tyrosinase and tannic acid on heat induced aggregation of natural actomyosin from sardine

The mixture of squid ink tyrosinase (SIT) at 300 and 500 U/g protein and tannic acid (TA) at 0.5 and 1% (based on protein) increased the turbidity and surface hydrophobicity of natural actomyosin (NAM) from sardine (Sardinella albella) in a dose dependent manner. Total sulphydryl group content decreased in the NAM solutions with coincidental increase in disulphide bond content, when added with SIT/TA mixture. Ca2+-ATPase activity was also lower in NAM solutions added with SIT/TA mixture. Higher aggregation of protein filaments was noticeable in NAM added with SIT at 500 U/g protein and 1% TA, which also had the highest storage modulus (G′) and largest particle size. Negative charge of NAM was decreased when SIT/TA mixture was incorporated. Therefore the mixture of SIT and TA, particularly at higher level, could be used as the novel protein cross-linker in fish mince and surimi.

Study on microwave‐accelerated casein protein grafted with glucose and β‐cyclodextrin to improve the gel properties

SummaryThe effect of glycosylation treatment coupled with microwave heating (MH) on gel properties and structure change of casein were investigated. Conjugation was confirmed by electrophoresis. Protein disulphide bonds were broken by microwave irradiation to create an increase first and a decrease later in free sulfhydryl contents with time, thereby inducing subunit disaggregation. Also, the exposure of hydrophobic core residues was increased in MH‐treated casein, which brings about protein disaggregation and unfolding. It showed that graft reactions by MH had much faster than those by water bath heating (WH). The content of disulphide bonds is 7.2% and 6.0% in the casein–glucose and casein–β‐cyclodextrin, respectively, treated by MH which was reduced significantly than that of treated by WH. Moreover, MH can increase the hardness of the gel. Consequently, MH could improve the efficiency of the reaction and gel properties.

Effect of hydrolysis time on the physicochemical and functional properties of corn glutelin by Protamex hydrolysis

The physicochemical and functional properties, such as surface hydrophobicity, disulphide bond content, thermal properties, molecular weight distribution, antioxidant properties, of corn glutelin hydrolysates catalysed by Protamex at different hydrolysis times were evaluated. The hydrolysis influenced the properties of corn glutelin significantly, and not only decreased its molecular weight and disulphide bond content, but also eventually transformed its insoluble native aggregates to soluble aggregates during the hydrolysis process. Corn glutelin hydrolysates were found to have a higher solubility, which was associated with their relatively higher foaming and emulsifying properties compared to the original glutelin. Corn glutelin and its hydrolysates maintained a high thermal stability. In addition, the hydrolysates exhibited excellent antioxidant properties measured through in vitro assays, namely DPPH and OH radical scavenging activity, Fe2+-chelating capacity and reducing power; the values were 58.86%, 82.64%, 29.92% and 0.236% at 2.0mg/mL, respectively.

Antibacterial Peptides from Plants: What They Are and How They Probably Work

Plant antibacterial peptides have been isolated from a wide variety of species. They consist of several protein groups with different features, such as the overall charge of the molecule, the content of disulphide bonds, and structural stability under environmental stress. Although the three-dimensional structures of several classes of plant peptides are well determined, the mechanism of action of some of these molecules is still not well defined. However, further studies may provide new evidences for their function on bacterial cell wall. Therefore, this paper focuses on plant peptides that show activity against plant-pathogenic and human-pathogenic bacteria. Furthermore, we describe the folding of several peptides and similarities among their three-dimensional structures. Some hypotheses for their mechanisms of action and attack on the bacterial membrane surface are also proposed.

Effect of Treating of Squid with Sodium Chloride in Combination with Oxidising Agent on Bleaching, Physical and Chemical Changes During Frozen Storage

Pink discolouration is a problem faced in the squid processing industry, and some treatments have been implemented to tackle such a problem. The study aimed to elucidate the impact of NaCl in combination with oxidising agents on the quality changes of squid during frozen storage. The effects of treatment of pink squid using 3% (w/v) NaCl solution containing oxidising agents (0.05–0.5% (w/v) H2O2 or 0–10 ppm NaOCl) on colour and chemical and physical changes of squid during frozen storage were investigated. The lowest decreases in a*, b* values, ∆E* and ∆C* of squid were obtained with the treatment using 3% NaCl solution containing 0.5% H2O2. Nevertheless, NaOCl (0–10 ppm) had no impact on a* and b* values. During frozen storage at −18 °C for 10 weeks, fresh squid, pink squid samples without and with treatments with 3% NaCl solution containing 0.5% H2O2 had no changes in a* and b* values during frozen storage. Nevertheless, thiobarbituric acid reactive substances value, disulphide bond content, thaw drip and shear force were more pronounced in treated pink squid, compared with pink squid without treatment (control) and fresh squid, respectively, during the extended storage (p < 0.05). Higher denaturation and aggregation of muscle proteins during frozen storage were observed in treated pink squid than that without treatment and fresh squid, respectively. Therefore, pink squid treated with oxidising agent was prone to protein aggregation and denaturation during the extended frozen storage, though it could lower the pink colour. Therefore, fresh squid without treatment using oxidising agent is recommended for production of frozen squid with negligible loss in quality during extended storage.

The efflux pump inhibitory properties of (thiolated) polyallylamines

The aim of this study was to investigate efflux pump inhibition by the cationic, non-biodegradable polymer poly(allylamine hydrochloride) and thiolated derivatives, using rhodamine-123 as model substrate. N-acetylcysteine (NAC) was covalently attached to poly(allylamine hydrochloride) (PAH) with a molecular mass of 15 kDa, 70 kDa and to a cross-linked derivative (cPAH). The resulting thiomers were characterized regarding thiol group and disulphide bond content, permeation enhancement across rat intestinal mucosa and safety. Permeation studies showed an up to 1.4-fold improved rhodamine uptake in the presence of 0.5% (m/v) unmodified PAHs. In contrast, an even 1.8-fold improved uptake was achieved in the presence of the corresponding thiomers. Histological observations led to the conclusion that safety of the polymer was not compromised by thiolation. According to these results the thiolated PAH turned out to be a safe tool for oral drug delivery enhancing permeation across the intestinal membrane.

Acid-induced gelation of natural actomyosin from Atlantic cod ( Gadus morhua) and burbot ( Lota lota)

The acid-induced gelation of natural actomyosin (NAM) from burbot ( Lota lota) and Atlantic cod ( Gardus morhua) added with d-gluconic acid- δ-lactone (GDL) during incubation at room temperature (22–23 °C) for 48 h was investigated. During acidification, pH values of both NAMs reached 4.6 within 48 h. Both NAMs underwent aggregation during acidification as evidenced by increases in turbidity and particle size, especially after 6 h of incubation. The decreases in Ca 2+-ATPase activity and salt solubility of both NAMs were observed during incubation. Decreases in total sulphydryl content with the concomitant increases in disulphide bond content of NAM from both species were also noticeable. Additionally, surface hydrophobicity of NAM increased, suggesting the conformational changes in NAM induced by acidification. The storage modulus ( G′) values increased with increasing incubation time and G′ development was greater in Atlantic cod NAM, compared with burbot NAM. Differential scanning calorimetry (DSC) revealed that T max and enthalpy of myosin peak shifted to the lower values and endothermic peak of actin completely disappeared. In general, gel development was more pronounced in Atlantic cod NAM, compared with the burbot counterpart. As visualised by transmission electron microscopy, network strands of aggregates from Atlantic cod were finer and more uniform than those of the burbot counterpart. Acid-induced gelation of NAM from both fish species therefore involved both denaturation and aggregation processes. However, gelation varied with fish species and had an impact on the resulting gels.

Preliminary work on the development of a novel detection method for osteoporosis

Osteoporosis affects both the organic and mineral phases of bone resulting in a decrease in resistance to fracture. Dual x-ray absorptiometry (DEXA) scans are used for diagnosing osteoporosis, which is conventionally characterised by a decrease in mineral density. Unfortunately, some patients who suffer osteoporotic fractures have normal bone density, because both the organic and the mineral phase are affected. However, there are currently no methods of evaluating the health of the organic phase. Patients undergoing treatment for osteoporosis have reported hardening of their fingernails. As the properties of nail and bone may be linked in a comparable, measurable way, this work used both mechanical (nano-indentation) and chemical (Raman spectroscopy) methods to evaluate differences between fingernails sourced from osteoporotic and non-osteoporotic patients. The difference in mean modulus between the nails sourced from the groups was 1.1 GPa. The disulphide bond content of fingernail samples from each group was measured by Raman spectroscopy and disulphide bond content of fingernail was found to be significantly lower in the osteoporotic group. It can be concluded that a relationship between the mechanical and chemical properties of nail and bone may exist in a measurable way. This work has suggested that changes in the organic phase of bone are reflected in similar proteins, such as keratin, from which fingernails are composed. Collagen and keratin are two distinct structural proteins, but they share the need for protein sulphation and disulphide bond formation, via cysteine, for their structural integrity. A disorder of either process should lead to disordered collagen and keratin synthesis.

A Study of Wool Carbonizing

During the time delay in rapid carbonizing, the distribution of sulfuric acid between surface acid and total acid inside the wool changes. At zero time delay there is 2.3% owf surface acid and 2.1% owf total acid inside the wool, while after 15 minutes delay the surface acid has dropped to 0.7% owf and the total acid inside the fiber has increased to 3.7% owf. Within the wool, the bound acid increases from 1.2% owf to 3.0% owf, leaving only 0.7% owf free acid inside the wool. Thus the amount of concentrated acid formed during drying and baking is minimized and less chemical attack occurs to wool in rapid carbonizing. The reduced chemical attack is indicated by a lower amino group content and a significantly higher disulphide bond content for rapidly carbonized wool compared with conventionally carbonized wool. These results show that there is both a reduced main chain and disulphide bond breakdown in rapidly carbonized wool. In the time range examined in this work, 10 minutes seems to be the optimum delay time. For delay times greater than 10 minutes, the delay is neither industrially practicable nor is the quality of the carbonized wool optimized.

Isolation and characterization of the perforatorium of rat spermatozoa

The perforatorium of rat spermatozoa was isolated and its protein composition determined. SDS-polyacrylamide gel electrophoresis showed that the organelle is composed of a single polypeptide component with a molecular weight of 13,000. The perforatorium becomes more resistant to solubilization during epididymal transit due to an apparent increase in disulphide bond content. Amino acid analysis of the perforatorium polypeptide revealed a content of 6-5% cysteine.

Preparation and analysis of peptide fragments produced by pepsin hydrolysis of human plasma albumin and their relationship to its structure.

Human plasma albumin was prepared and subjected to proteolysis by pepsin at pH2.45 at 25 degrees for 10min. with albumin/pepsin ratio 3000:1. Five peptide fragments were detected in the proteolysate by means of zone electrophoresis and gel filtration; these were separated and purified. Molecular weights, amino acid composition and disulphide bond content of the purified fragments were determined. The results show that a high proportion of the polypeptide chain of albumin appears to have a low cystine content, and at low pH values the molecule would be expected to have a considerable degree of freedom in its structure in these regions of the chain. A tripartite model for the structure of plasma albumin is proposed.

Role of Disulphide Bonds in the Resistance of Bacillus cereus Spores to Gamma Irradiation and Heat

Summary. Spores of Bacillus cereus were treated with thioglycollic acid which ruptures at least 10–30% of the spore disulphide bonds by reducing them to thiol groups. The treated spores were still viable and were sensitive to lysozyme but remained as resistant to γ‐irradiation and to heat as untreated spores. Neither treated nor untreated spores were sensitized to irradiation by reagents which block thiol groups. The results did not indicate that the high content of disulphide bonds in spore coat protein protects spores against inactivation by irradiation or heat.

SENSITIZATION OF BACTERIAL SPORES TO LYSOZYME AND TO HYDROGEN PEROXIDE WITH AGENTS WHICH RUPTURE DISULPHIDE BONDS.

SUMMARY: Spores of Bacillus and Clostridium species were subjected to oxidizing and reducing agents known to rupture protein disulphide bonds and to irradiation (ultraviolet; high speed electron). These treatments caused no loss of brightness of spores when viewed by phase-contrast microscopy. However, lysozyme or hydrogen peroxide caused phase darkening of treated spores and loss of dipicolinic acid typical of normal germination except that hydrogen peroxide eventually caused almost complete lysis of the spores. Under certain conditions, spore viability was unaffected during treatment with reducing agents and during subsequent phase darkening in lysozyme. Spores made susceptible to lysozyme by reducing agents became insusceptible after storage in aerated water. These reactions are compatible with Vinter's observation of the high content of disulphide bonds in the coat fraction of spores (Vinter, 1960) and with the chemical or physical rupture of these bonds. Rupture of disulphide bonds allows action of lysozyme or hydrogen peroxide on previously protected substrates. The disulphide bonds are therefore probably important in the resistance of spores to enzymes and irradiation, and rupture of these bonds may be involved in the germination process. The probable location of the lysozyme substrate in mucopeptide of the spore cortex indicates the importance of the integrity of cortex structure in maintaining the phase brightness of spores.