Proportion Of Peptides Research Articles

Effect of NaCl partial replacement by KCl, Ca-ascorbate, and spent hen meat hydrolysate on the physicochemical properties and quality of Cantonese sausage.

A large amount of NaCl is usually used to provide a unique flavor and extend the shelf life of meat products. However, excessive sodium intake may cause diseases such as cardiovascular diseases. Spent hen meat hydrolysate (SHH) as an efficient NaCl substitute was developed with inefficient research related to SHH application in food systems. Therefore, the effects of NaCl replacement with SHH, KCl, and Ca-ascorbate on the quality of low-sodium Cantonese sausage were investigated. Four groups of salt formulation, I (100% NaCl), II (NaCl/KCl/Ca-ascorbate=60%/30%/10%), III (NaCl/KCl/Ca-ascorbate/SHH=50%/30%/10%/10%), and IV (NaCl/KCl/Ca-ascorbate/SHH=30%/30%/10%/30%), were used to produce Cantonese sausages. The moisture and nitrite content decreased, the microbiological growth was inhibited, and the protein content increased after adding SHH for Cantonese sausages with NaCl substitution degrees of 50% and 70%. The saltiness, overall flavor, color, and texture of low-sodium Cantonese sausages with SHH were maintained or improved compared to the Cantonese sausage without sodium replacement. The proportion of peptides with molecular weight<1kDa in Cantonese sausages increased after adding SHH, which may improve the overall flavor by interacting with peptides or other compounds. SHH combined with KCl and Ca-ascorbate is an efficient NaCl substitute, which can maintain and even improve Cantonese sausage quality and reduce sodium content up to 70%. These findings offer a promising reference for SHH application in the food industry and promote the development of salt taste-enhancing hydrolysate in food science.

High-intensity ultrasound promoted the maturation of high-salt liquid-state soy sauce: A mean of enhancing quality attributes and sensory properties

High-intensity ultrasound was used as a means to promote maturation of soy sauce. The optimal conditions for ultrasound treatment were 90℃ at an ultrasound intensity of 39.48 W/cm2 for 60 min. The total reducing sugars and soluble salt-free solids content was significantly increased after ultrasound-assisted maturation. The free amino acid content was significantly decreased, mainly due to the Maillard reaction (MR). The promoted MR produced several types of flavor compounds, including esters, pyrazines, and ketones, which imparted an attractive aroma to the maturated soy sauce. The proportion of peptides with a molecular weight of 1–5 kDa provided umami as an important flavor characteristic, and the content in the ultrasound-matured soy sauce (10.19 %) was significantly higher than that in the freshly prepared soy sauce (8.34 %) and the thermally treated sample (8.89 %). Ultrasound-assisted maturation would improve product quality and meanwhile, shorten the duration and reduce the cost for the soy sauce industry.

Extensive hydrolysis of milk protein and its peptidomic antigenicity analysis by LC-MS/MS.

Milk protein concentrate (MPC) is considered an ideal substitute of cow milk because of its similar protein and nutrition. In this study, MPC was hydrolyzed to peptides by alcalase and neutrase, and the properties of hydrolysate were evaluated. When MPC was hydrolyzed at the ratio of alcalase and neutrase of 1:1 and enzyme to substrate ratio of 6000U/g MPC at 50°C, pH 8.5 for 3h, the proportion of peptides with molecular weights <1kDa was 85.31%, and the antigenicity reduction rates of casein and β-lactoglobulin were 33.76% and 22.38%, respectively. Moreover, LC-MS/MS peptide identification revealed that the alcalase and neutrase disrupted a total of 65 epitopes of casein and 21 epitopes of whey protein, which further elucidated the mechanism of complex enzyme hydrolysis to reduce milk protein allergenicity.

Comparison of the generation of α-glucosidase inhibitory peptides derived from prolamins of raw and cooked foxtail millet: In vitro activity, de novo sequencing, and in silico docking

Foxtail millet prolamin has been demonstrated to have anti-diabetic effects. In this study, we compared the generation of anti-α-glucosidase peptides derived from prolamins of raw and cooked foxtail millet (PRFM and PCFM). PRFM and PCFM hydrolysates (PRFMH and PCFMH) both exhibited α-glucosidase inhibitory activity. After ultrafiltration according to molecular weight (Mw), the fraction with Mw < 3 kDa in PCFMH (PCFMH<3) showed higher α-glucosidase inhibitory activity than that in PRFMH (PRFMH<3). The composition of α-glucosidase inhibitory peptides identified by de novo sequencing in PCFMH<3 and PRFMH<3 was compared by virtual screening, combining biological activity, net charge, grand average of hydropathicity (GRAVY), and key hydrophobic amino acids (Met, Pro, Phe, and Leu). We found that the proportion of peptides with excellent α-glucosidase binding force in PCFMH<3 was higher than in PRFMH<3. Overall, cooking may positively affect the generation of peptides that perform well in inhibiting α-glucosidase derived from foxtail millet prolamin.

Characteristics of the microstructure and the key components of white kidney bean sourdough bread induced by mixed-strain fermentation and its influence on gut microbiota.

In this study, the effect of mixed-strain fermentation using Kluyveromyces marxianus with either Lactobacillus plantarum or Pediococcus pentosaceus on the physiochemical and nutritional properties of white kidney bean flour sourdough was investigated. The results indicated that mixed-strain fermentation reduced the anti-nutritional factors produced from the white kidney bean flour, especially in the sourdough fermented by L. plantarum and K. marxianus (WKS-LK) compared to that by P. pentosaceus and K. marxianus (WKS-JK). Meanwhile, the content of lactic acid and acetic acid and the proportion of peptides with molecular weights ranging from <500 to 5000 Da were increased in the sourdoughs (WKS-LK > WKS-JK). Compared to the control (WK), microstructural characteristics of the dough seemed to be improved in WKS-LK followed by WKS-JK in terms of their corresponding gluten network consistency. Moreover, mixed fermentation led to a reduced starch digestibility accompanied by a higher content of resistant starch and slowly digestible starch. In contrast, protein digestibility was enhanced in WKS-LK and WKS-JK sourdough breads. More importantly, the changes in gut microbiota composition, short-chain fatty acid (SCFA) production, systemic inflammation, glucose tolerance and liver tissue histopathology following 21-day consumption of the sourdough bread were also evaluated via an animal model. The intake of sourdough breads reduced the abundance of the pathogenic microbiota Escherichia shigella. In contrast, the corresponding abundance of Rikenellaceae, Akkermansiaceae, Erysipelotrichaceae, Prevotellaceae and Eubacterium coprostanoligenes was increased, followed by enhanced SCFA generation, with the highest in WKS-LK and then WKS-JK. Meanwhile, a reduced level of pro-inflammatory cytokines IL-1β, IL-6 and TNF-α in the serum and improved glucose tolerance and liver tissue histopathology following the bread consumption were also achieved in the order of WKS-LK, then WKS-JK mice compared to WK.

Transcriptome Sequencing of the Pale Anemones (Exaiptasia diaphana) Revealed Functional Peptide Gene Resources of Sea Anemone

Sea anemone venom is a marine drug resource library with pharmacological and biotechnology value, and it contains complex and diverse functional peptide neurotoxins. However, the venom components of only a limited number of sea anemone species have been globally evaluated by transcriptomics and proteomics. In this study, 533 putative protein as well as peptide toxin sequences were found on a large scale from dissimilar developmental stages of sea anemone Exaiptasia diaphana, which can be divided into 75 known superfamilies according to the predicted functions. Among them, the proportion of protein is 72.98%, and its main families are metalloproteases, chymotrypsinogen like, collagen, pancreatic lipase-associated protein like, and G-protein coupled receptor, while the proportion of peptides is 27.02%, and main families are ShK domain, thrombin, Kunitz-type, defensin, as well as insulin-like peptide. Finally, typical anemone peptide neurotoxins were screened, and the 3D structure and pharmacological activity of these anemone peptide neurotoxins were predicted by homology modeling. We elucidate on a valuable high-throughput approach for obtaining sea anemone proteins and peptides. Our findings form the basis for targeted studies on the diversity as well as pharmacological effects of sea anemone peptide neurotoxins.

Equilibrium Constants of Interaction between Pyridoxal-5'-Phosphate Coenzyme and Glycine and Its Oligopeptides in Aqueous Buffered Saline

Electronic absorption spectroscopy is used to study the patterns of bonding of oligopeptides of glycyl-glycine and glycyl-glycyl-glycine using the coenzyme pyridoxal-5'-phosphate at 293 K in a phosphate buffer solution at pH 7.35. The results are compared to the similar process for monomeric glycine. The interaction constants and the spectral parameters of the reaction products are determined. The observed increase in the peptide–coenzyme bonding equilibrium constants in the Gly–(Gly–Gly)–(Gly–Gly–Gly) series is due to a drop in the basicity of the reaction’s amino group and an increase in the proportion of peptides with non-ionized amino groups in the solution. An increase in the chain length of the peptide is accompanied by a reduction in the coefficient of extinction of the resulting Schiff base.

Principal Physicochemical Methods Used to Characterize Dendrimer Molecule Complexes Used as Genetic Therapy Agents, Nanovaccines or Drug Carriers.

Nanomedicine is the application of nanotechnology to medicine. This field is related to the study of nanodevices and nanomaterials applied to various medical uses, such as in improving the pharmacological properties of different molecules. Dendrimers are synthetic nanoparticles whose physicochemical properties vary according to their chemical structure. These molecules have been extensively investigated as drug nanocarriers to improve drug solubility and as sustained-release systems. New therapies such as gene therapy and the development of nanovaccines can be improved by the use of dendrimers. The biophysical and physicochemical characterization of nucleic acid/peptide-dendrimer complexes is crucial to identify their functional properties prior to biological evaluation. In that sense, it is necessary to first identify whether the peptide-dendrimer or nucleic aciddendrimer complexes can be formed and whether the complex can dissociate under the appropriate conditions at the target cells. In addition, biophysical and physicochemical characterization is required to determine how long the complexes remain stable, what proportion of peptide or nucleic acid is required to form the complex or saturate the dendrimer, and the size of the complex formed. In this review, we present the latest information on characterization systems for dendrimer-nucleic acid, dendrimer-peptide and dendrimer-drug complexes with several biotechnological and pharmacological applications.

Дослідження здатності до протеолізу м’ясних січених напівфабрикатів функціонального призначення

Розроблено модельні рецептури м’ясних січених напівфабрикатів функціонального призначення із застосуванням м’яса курчат бройлерів, білкової емульсії на основі білків свинячої шкурки та сухої молочної сироватки, клітковини пшеничної гідратованої, концентрату зеленої маси подорожника та двох видів модифікованих жирів рослинного походження. Досліджено вплив внесення у рецептуру січених напівфабрикатів з м’яса птиці модифікованих жирів різного складу, рослинної сировини та клітковини гідратованої на здатність до протеолізу залежно від рецептурних співвідношень наведених компонентів. Здатність до протеолізу досліджена за допомогою ферментативного гідролізу під дію ферментів пепсину і трипсину в системі in vitro. При проведенні ферментативного гідролізу проаналізовано зразки, що містили в рецептурах білково-жирову емульсію на основі білків свинячої шкурки та сухої молочної сироватки із застосуванням двох видів модифікованих жирів, що містять відповідно ріпакову та пальмову олії як основний складовий компонент. Як контрольну групу прийнято зразки, що відрізнялись відсутністю рослинної сировини (концентрату зеленої маси подорожника) у рецептурі, а також зразки із внесенням білкової емульсії без застосування жиру. Як дослідні зразки представлено зразки модельних січених м’ясних напівфабрикатів із вмістом білково-жирової емульсії на основі білків свинячої шкурки та модифікованих жирів 22,5% з однаковим рівнем внесення гідратованої пшеничної клітковини та концентрату зеленої маси подорожника (18 і 2% відповідно). В ході проведених досліджень вимірювали рівень накопичення продуктів протеолізу у відібраних пробах гідролізату паралельно за двома методиками. Для фіксування гідролізу незамінних амінокислот використовували визначення вмісту тирозину за методом Лоурі. Для визначення загальної частки речовин пептидної та білкової природи у гідролізаті використовували біуретовий метод. За результатами досліджень встановлено, що у контрольних зразках на першій (пепсиновій) стадії протеолізу накопичується більше пептидних сполук, проте мало тирозину. У модельній групі зразків зафіксовано стабільну швидкість накопичення тирозину та перевищення кінцевого вмісту усіх пептидних сполук по завершенню повного циклу протеолізу.

Peptide profiling and the bioactivity character of yogurt in the simulated gastrointestinal digestion

This study investigated the relationship between peptide profiles and the bioactivity character of yogurt in simulated gastrointestinal trials. A total of 250, 434 and 466 peptides were identified by LC-MS/MS analyses of yogurt, gastric digest and pancreatic digest. Forty peptides of yogurt survived in gastrointestinal digestion. κ-CN and β-CN contributed the diversity of peptides during the fermentation process and gastrointestinal digestion, respectively. The favorite of κ-CN by lactic acid bacteria complemented gut digestion by hydrolyzing κ-CN, the low abundance milk proteins. The potential bioactivities were evaluated by in vitro ACE and DPP-IV inhibition assays. The ACE inhibition rate of the pancreatic digests was ~4 - and ~2 - fold greater than that of yogurt and the gastric digests. The ACE inhibitory peptides generated during gastrointestinal digestion improved the ACE inhibitory activity of the gastric and pancreatic digests. The DPP-IV inhibition rate of the pancreatic digest was ~6 - and ~3 - fold greater than that of yogurt and the gastric digest. The numbers of potential DPP-IV inhibitory peptides were positively correlated to the DPP-IV inhibitory activity of the gastric and pancreatic digests. Biological significanceThe present study describes the characters and bioactivities of peptides from yogurt in a simulated gastrointestinal digestion. The number of peptides identified from yogurt and gastrointestinal digests by LC-MS/MS increased in the simulated gastrointestinal trials. The in vitro ACE and DPP-IV inhibition bioactivities revealed that the bioactivity of yogurt was enhanced during gastrointestinal digestion. The correlation between peptides and bioactivity in vitro indicated that not only the peptides amount but also the proportion of peptides with high bioactivities contributed to increased bioactivity during gastrointestinal digestion. The study of peptides identified from yogurt and digests revealed that the number of released peptides was not determined by the abundance of the parent proteins but by whether the enzymes favored the protein.In summary, peptide profiling and bioactivities of yogurt in simulated gastrointestinal digestion helped to elucidate the health benefits of yogurt peptides. The results further revealed that pre-digestion of milk by lactic acid bacteria are complementary to generate bioactive peptides and to provide particular yogurt functions.

Impact of ultrasound on egg white proteins as a pretreatment for functional hydrolysates production

The objective of this study was to investigate the effects of different ultrasound pretreatment on enzymatic hydrolysis of egg white proteins (EWPs) by Alcalase as well as evaluating some functional and antioxidant properties of hydrolysates obtained by various proteases treatment and ultrasound technology. The effects of chosen ultrasound pretreatment parameters including frequency of ultrasonic waves (35 and 40 kHz), temperature (25 and 55 °C), time of pretreatment (15–60 min) and pH of egg white solution (7.00–10.00) were examined. It appeared that controlled ultrasound treatment can improved the hydrolysis process compared with untreated samples, but optimization of the power and length of sonication was important. The optimal ultrasound pretreatment at calorimetric power of 21.3 W and frequency of 40 kHz for 15 min at 25 °C and with naturally basic egg white (pH 9.25) resulted in increased initial rate and equilibrium degree of Alcalase hydrolysis by about 139.8 and 13.86 % compared with the control, respectively. EWP hydrolysates with ≈27.0 % degree of hydrolysis obtained with heat pretreatment and ultrasound pretreatments under optimal conditions were further separated by sequential ultrafiltration into 4 hydrolysate fractions ( 30 kDa) which were investigated for protein content, peptide yield and antioxidant activity. The hydrolysis after heat pretreatment generated more peptides <1 kDa (19.04 ± 1.02 %) than ultrasound pretreatment did (11.90 ± 0.53 %), whereas the proportion of peptides <10 kDa were higher in the second case (28.80 ± 0.07 vs. 20.46 ± 0.39 %). The fraction obtained by the ultrasound pretreatment containing peptides with a molecular weight between 1 and 10 kDa demonstrated the strongest ABTS radical scavenging efficacy among the fractions (97.54 ± 0.30) with IC50 value of 4.31 mg/mL. Compared with single-enzyme processes, the two-stage enzymatic processes did not significantly improve both antioxidant and functional hydrolysates’ properties.

Characterization of peptides in ensiled alfalfa treated with different chemical additives

Effects of different chemical additives on peptide composition in ensiled alfalfa (Medicago sativa L.) were investigated by using gel filtration and determination of N characteristics. The alfalfa silages were prepared untreated (control) or with formic acid, formaldehyde or tannic acid as additives at ensiling. All additives reduced non-protein N (NPN), ammonia nitrogen (NH3 -N) and amino acid N (AA-N) in the ensiled forage, and the most effective reduction of NPN and AA-N was observed in the formaldehyde-treated silages. Peptides in the control silage were mainly dipeptides to peptides with five amino acid residues. Most peptides in the formic acid-treated silage contained 4-12 amino acid residues. Although most peptides in the formaldehyde-treated silages contained 4-6 amino acid residues, there was a considerable proportion of peptides with 7-11 amino acid residues. Tannic acid had little effect on peptide size of ensiled alfalfa extract in which most peptides contained 5-6 amino acid residues. Peptide size in formic acid-treated alfalfa silage was greater than that in the other treatments. Addition of formic acid and formaldehyde not only increased the peptide concentration in alfalfa silage, but enlarged the peptide size.

Antioxidant activities of rapeseed peptides produced by solid state fermentation

In this study, rapeseed peptides (RPs) were prepared by solid state fermentation with Bacillus subtilis followed by evaluation of peptide antioxidant activities (scavenging of DPPH, ferric reducing power, ferrous ion-chelation and ability to inhibit linoleic acid autoxidation, in vitro). The content of soluble peptides increased rapidly within the first 2days of fermentation, which suggested high susceptibility of the rapeseed proteins to microbial proteases. After 3days of fermentation, RPs were composed mainly of five peptide fractions within the 180–5500Da size range; however, proportion of peptides with <3000Da size decreased significantly (p<0.05) after 5days of fermentation. Glutamic acid (19.5%), lysine (7.6%) and proline (7.3%) were the most dominant amino acids present in the RPs but serine (1.5%), tryptophan (1.3%) and cysteine (0.5%) were present in least amounts. A concentration-dependent effect on antioxidant activities was present in RPs, which showed high activities of scavenging free radical, reducing power, and inhibition of lipid peroxidation, but low ferrous ion-chelating activity. We concluded that fermentation provided a suitable medium for converting rapeseed meal into antioxidant peptides that may be used to formulate functional foods and nutraceuticals.

Biophysical Studies Of The Membrane Interactions Of A Transthyretin Fragment TTR(10-20)

TTR(10-20) is a peptide derived from transthyretin, a 127 amino acid amyloid protein. Previous studies on TTR(10-20) have shown that this peptide could form protofibrils and fibrils in vitro. These are very rich β-sheet structures, insoluble at physiological pH. In vivo, protofibrils and fibrils deposit on tissues and lead to degenerescence. The goal of the present study is to characterize peptide structure and membrane interactions using different spectroscopic techniques.The secondary structure of TTR(10-20) was determined by Fourier transform infrared (FTIR) spectroscopy. More specifically, the information about the peptide secondary structure is given by the amide I band, which was monitored as a function of temperature and lipid composition of the bilayer. On most spectra, there is an aborption band around 1620 cm−1, corresponding to an intermolecular β-sheet structure such as protofibrils and fibrils. The area of this band increases with increasing temperature while the band corresponding to disordered structures decreases. The nature of the lipid head group also appears to have an impact on the aggregation of TTR(10-20).The lipid bilayer is also affected by the presence and the proportion of peptide. Solid-state 31P and 2H nuclear magnetic resonance spectroscopy were used in the present study to determine the location of the peptide in the bilayer. More specifically, 31P NMR is used to investigate the effect of TTR(10-20) on the lipid head group while 2H NMR is used to investigate the effect of the peptide on the lipid acyl chains.

Portal Absorption of Feed Oligo-peptides in Chickens

The effect of duodenal infusion with feed oligo-peptide solution on portal absorption of amino acids was investigated in poultry under unanaesthetized conditions. Four peptide solutions were used in the experiment: enzymatic hydrolysates from fish meal, soybean meal, cottonseed meal and rapeseed meal proteins with average molecular weights less than 3,000 Da and 1,000 Da, respectively. Intestinal absorptions of these oligo-peptide solutions were compared by determining the concentration of free amino acid (FAA) in portal blood after the duodenal administrations of oligo-peptide solutions. Absorptive intensity and balance were used to estimate the intestinal absorption rate of amino acids. The absorptive intensities of amino acids were highest for the fish and soybean meal oligo-peptides. The ratios of amino acids absorbed in the portal blood from fish and soybean meal oligo-peptides were more similar to the composition of the infused amino acids than that observed from the cottonseed and rapeseed meal oligo-peptides. A positive correlation was found between absorption rate and proportion of PAA in the oligo-peptides. The higher absorption rate could be contributed to the higher proportion of peptide bound amino acids (PAA). The results suggest that fish and soybean meal protein are significantly more easily hydrolyzed into oligo-peptides (p<0.05) in the gastrointestinal tracts of poultry and as such can be utilized more effectively by body tissues. (Asian-Aust. J. Anim. Sci. 2004. Vol 17, No. 9 : 1277-1280)

Post-translational modification of nisin. The involvement of NisB in the dehydration process.

The lantibiotic nisin is an antimicrobial peptide produced by Lactococcus lactis. As with all lantibiotics, nisin contains a number of dehydro-residues and thioether amino acids that introduce five lanthionine rings into the target peptide. These atypical amino acids are introduced by post-translational modification of a ribosomally synthesized precursor peptide. In certain cases, the serine residue, at position 33 of nisin, does not undergo dehydration to Dha33. With native nisin this partially processed form represents about 10% of the total peptide, whereas with the engineered variants, [Trp30]nisin A and [Lys27,Lys31]nisin A, the proportion of peptide that escapes full processing was found to be to approximately 50%. This feature of nisin biosynthesis was exploited in an investigation of the role of the NisB protein in pre-nisin maturation. Manipulation of the level of NisB was achieved by cloning and overexpressing the plasmid-encoded nisB gene in a range of different nisin-producing strains. The resulting fourfold increase in the level of NisB significantly increased the efficiency of the dehydration reaction at Ser33. The final secreted product of biosynthesis by these strains was the homogenous form of the fully processed nisin (or nisin variant) molecule. The results presented represent the first experimental evidence for the direct involvement of the NisB protein in the maturation process of nisin.

Influencia de las condiciones de elaboración sobre la proteolisis durante la maduración del jamón ibérico Influence of the processing conditions of Iberian ham on proteolysis during ripening

Non-protein nitrogen and its fractions (peptides, amino acids and volatile basic nitrogen) were determined in biceps femoris and semimembranosus muscles of two homogeneous groups of Iberian dry-cured ham in different stages of maturation, and ripened in two different factories under different environmental conditions. A progressive increase in non-protein nitrogen was observed during ripening in all groups, being especially intense during the drying stage, when the temperature was the highest during maturation. During the first stages of processing, the proportion of peptides and free amino acids remained similar while free amino acids increased more markedly from the drying stage, representing the largest fraction at the end of the process. Volatile basic nitrogen was the least abundant fraction of non-protein nitrogen during ripening. Hams kept at higher temperature during longer periods, and with lower salt content, produced larger amounts of all three fractions of non-protein nitrogen in fully ripened dry-cured Iberian ham.

Effects of abomasal infusions of sodium caseinate and of casein hydrolysates varying in the relative proportions of peptides and free amino acids on milk production in dairy cows.

Two experiments were conducted to test the hypothesis that responses of milk production to the abomasal infusion of casein or hydrolysates of casein can be influenced by the proportion of peptide-bound amino acids in the infusate. Eight lactating cows were used in two Latin square experiments with period lengths of 10 d. In Expt 1, the four cows were at a late stage of lactation and the four treatments were a basal diet of silage and a barley-soya supplement alone or with infusions into the abomasum of 180 g/d of sodium caseinate, an enzymic hydrolysate of casein or an acid hydrolysate of casein; all treatments supplied equivalent amounts of all the amino acids, this being achieved by addition of free amino acids as required. As infused, the three treatments contained 89 (caseinate), 40 (enzymic hydrolysate) and 15 (acid hydrolysate) % of their amino acids as peptides. The increase of milk production in response to infusion was small and there were no significant differences between the infusion treatments. In Expt 2, the cows received a basal diet of grass silage and a supplement containing feather meal as the main source of protein. Treatments were the basal diet alone and with three infusion treatments as in Expt 1, except that the amount infused was 230 g/d. The response to infusion was greater in this experiment, there were significant differences between infusions and the yield of milk protein with the infusion treatments was linearly related (P = 0.001) to the proportion of peptide-bound amino acids in the infusate. Moreover, there was a close inverse relation (P = 0.007) between the proportion of peptide-bound amino acids in the infusate and the concentration of total peptide-bound amino acids in blood plasma.

The macromolecular properties of blood-group-specific glycoproteins. Characterization of a series of fractions obtained by solvent fractionation.

1. The glycoprotein components of a human ovarian-cyst fluid were isolated by a solvent [95% (w/w) phenol]-extraction procedure; the phenol-insoluble water-soluble glycoprotein was further fractionated by (NH(4))(2)SO(4) and by ethanol to yield eight fractions. 2. The fractions were analysed in terms of amino acids, fucose, galactose, N-acetylglucosamine, N-acetylgalactosamine and sialic acid. Variations occurred, particularly in the proportion of peptide; these were partly correlated with varying extent of serological activity. 3. The fractions were characterized physicochemically in terms of buoyant density and degree of spreading in a density gradient, sedimentation velocity and molecular weight; their partial specific volumes and specific refraction increments were also determined. 4. The fractions showed wide variations in their sedimentation-velocity and density-gradient patterns, and gave evidence of pauci-dispersity in density. The fraction regarded as the most typical blood-group-specific glycoprotein sedimented as a single rapidly spreading peak and was of high molecular weight. 5. Significant correlations were observed between the physical properties of the glycoprotein fractions and the amount of their peptide component. The buoyant densities and sedimentation coefficients varied in a manner that suggested the existence of two families of glycoproteins. 6. It is suggested that variability in the extent of glycosylation, or in the degree of cross-linking, might account for the two families of glycoproteins, and that the extent of cross-linkage might also be a factor determining the solubility of these glycoproteins in hot saturated (NH(4))(2)SO(4).