[7] Determination of amide residues by chemical methods

Purification and Characterization of a New Lectin from Loach Skin Mucus

Lectin from loach skin mucus plays an important role in pathogen defense. However, hardly can any paper relevant to the character of lectin from loach skin mucus be found in recent years. In this study, a kind of new lectin (LML), with a high hemagglutination activity of 166.23 × 103 HU/mg, was successfully isolated and purified from loach skin mucus. LML was a kind of glycoprotein with a molecular weight of 245 kDa. Also, the monosaccharide composition suggested that its carbohydrate chain was composed of rhamnose, arabinose, xylose, mannose, glucose, and galactose with a molar ratio of 2.02 : 11.66 : 2.06 : 1.00 : 14.09 : 6.00. Besides, LML depended on Ca2+to induce hemagglutination and was strongly inhibited by D-lactose. The lectin exhibited powerful resistance to alkali and kept about 30% hemagglutination activity at pH 14.0, whereas its capacity of acid resistance was weak. The maximum hemagglutination activity of LML maintained at a temperature range from 20°C to 50°C. Moreover, the structure of LML was preliminarily studied, indicating it contained abundant glutamic acid, histidine, and serine, and its secondary structure containedα-helix (4.97%),β-sheet (27.55%), turns structure (49.78%), and unordered structure (17.70%).

Delayed-onset muscle injury and its modification by wheat gluten hydrolysate

OBJECTIVE

We investigated the pattern of delayed-onset muscle injury in well-trained athletes after a competitive half-marathon and the effects of post-race intake of wheat gluten hydrolysate (WGH).

METHODS

Thirty well-trained college runners with a best time of 14-15 min over 5000 m raced in a half-marathon. Thereafter, they were divided into three groups based on finish times and given 0 (control), 10, or 20 g of WGH. Blood biochemical parameters were monitored at -1 d, +1 h, +1 d, and +2 d after the race. Data selected according to finish times and biochemical parameters were then analyzed.

RESULTS

Plasma creatine kinase activity peaked at 1 d after the race in the control group and correlated with post-race white blood cell counts. The post-race elevation of creatine kinase activity was dose-dependently suppressed by WGH.

CONCLUSION

Delayed-onset muscle injury peaked in well-trained distance runners at 1 d after a half-marathon and was dose-dependently suppressed by a post-race intake of WGH.

Glutamine content of protein and peptide-based enteral products

BACKGROUND

Glutamine is a conditionally essential amino acid for patients with severe catabolic illness, intestinal dysfunction, or immunodeficiency syndromes. Glutamine is a natural component in many enteral preparations, yet lacking methodology hampers its quantitative determination in dietary products.

OBJECTIVE

The present study was assigned to assess glutamine contents in selected enteral products by using a newly developed method enabling the assessment of protein/peptide bound glutamine.

METHODS

Fourteen commercially available enteral diets (10 protein based and 4 peptide based) were investigated. After removal of interfering fat and carbohydrates, the nitrogen content of the purified preparations was determined by chemiluminescence and protein/peptide bound glutamine was assessed using a three-step procedure; by using a novel prehydrolysis derivatization technique with bis(1,1-trifluoroacetoxy)iodobenzene, glutamine is converted to acid stable diaminobutyric acid. The derivatives are hydrolyzed with a new microwave technology, and subsequently the amino acid composition is determined by reversed phase-high-performance liquid chromatography after dansyl-chloride derivatization.

RESULTS

The content in the protein-based preparations varied between 5.2 and 8.1 g/16 g nitrogen. In the peptide-based products, considerably lower glutamine contents were measured (1.3 to 5.6 g/16 g nitrogen).

CONCLUSION

In the present study, we report for the first time glutamine contents in ready to use enteral products. The daily amount might be satisfactory for healthy individuals but probably not sufficient for the adequate support of the stressed patient. Reliable assessment of glutamine in enteral formulae is a prerequisite t perform clinical studies investigating glutamine requirements in the catabolic state.

Effect of an enterally administered glutamine-rich protein on the catabolic response to a zymosan challenge in rats

Glutamine is considered to be a conditionally essential amino acid during critical illness and has, therefore, been advocated to be included in nutritional support supplied in these situations. We investigated whether a diet containing a protein source rich in glutamine can restore depleted glutamine pools (plasma and muscle) and counteract muscle wasting, in a rat model of critical illness (intraperitoneal injection of zymosan). A glutamine-rich protein source was obtained by mixing a wheat protein hydrolysate (25% glutamine) with a whey protein isolate (to prevent essential amino acid deficiency). Feeding healthy control rats for 2 weeks with an adequate diet containing this protein source increased the two main glutamine pools (plasma and muscle). However, no effect was observed on the following zymosan-induced changes: 1) decreased glutamine and arginine concentrations (plasma and muscle), 2) wasting of muscle protein, and 3) decreased mitochondrial content in skeletal muscle. We conclude that a diet containing a glutamine-rich protein source can be used to increase plasma and muscle glutamine concentrations in healthy rats, but is of limited value to counteract wasting of skeletal muscle in zymosan-treated rats.

Deamidation of food proteins to improve functionality

Many proteins, particularly those in plants, require structural modifications to improve their functional properties for expanded use. Several chemical and enzymatic methods are described for food protein deamidation to improve solubility, emulsification, foaming, and other functional properties of the proteins. The use of enzymes in protein modification is more desirable than chemical treatments because of their speed, mild reaction conditions, and their high specificity. Transglutaminase, protease, and peptidoglutaminase (PGase) are the only enzymes reported in the literature for protein deamidation. Of these, PGase appears to be the most feasible for practical application. PGase production, purification, and use in deamidation are discussed.

Protein deamidase from germinating wheat grains

A new enzyme catalyzing the deamidation of seed storage proteins was found in germinating wheat grains and was partially purified. It also acts on egg lysozyme, horse hemoglobin and reduced RNAse, glutamine and Gly-L-Gln-L-Tyr. No activity was observed when using ovalbumin, serum albumin, RNAse, insulin, asparagine and an asparagine-containing peptide. Only glutaminyl residues appear to be deamidated by this enzyme. It differs from transglutaminase and proved to be a true protein deamidase.

A vitamin-K2-binding factor secreted from Bacillus subtilis

The synthesis of vitamin K2 by Bacillus subtilis was found to increase in parallel with the number of cells. In the exponential growth phase, most vitamin K2 was found in the bacterial cells. At the end of the growth phase, however, the soluble form of vitamin K2 appeared in the incubation media and amounted to 40% of the total vitamin K2 at the stationary phase. DEAE ion-exchange chromatography of the incubation medium showed a single elution peak corresponding to vitamin K2, suggesting the secretion of vitamin K2 in the form of a soluble complex with a specific acidic binding factor. This factor was partially purified by consecutive DEAE chromatography, and examined by polyacrylamide disc gel electrophoresis. A band stainable with acridine orange, a cationic dye, was found to co-migrate with vitamin K2. This band was also visualized by periodic acid/Schiff staining. Gel-permeation chromatography showed that the binding factor in its active form has an apparent molecular mass of 100 kDa and is capable of binding exogenous menaquinone but not menadione. Chemical analysis indicated that this binding factor contained about 20% carbohydrate and 80% peptide which consisted mainly of Leu, Glu, Asp and Val. The new acidic glycoconjugate was designated as the vitamin-K2-binding factor.

Trypsin activation of enterotoxin from Clostridium perfringens type A: fragmentation and some physicochemical properties

Clostridium perfringens type A enterotoxin was activated about 3-fold by treatment with trypsin, without an observed change in molecular weight. On denaturation in 8 M urea, the trypsinated enterotoxin lost a small peptide of about 4000 daltons. The single cysteine residue of enterotoxin was in the small peptide together with seven out of nine residues of proline. Trypsin activation, without removal of the small peptide, increased the 'outside' number of amino groups from eight to eleven. The trypsin treatment of the enterotoxin did not change the antigenic properties of the protein. Glycine was the C-terminal residue of the native enterotoxin while the dansyl alpha-amino acid of the N-terminal could not be identified.

Isolation of Desulfuromonas acetoxidans cytochrome c-551.5 from the mixed culture 'Chloropseudomonas ethylica'

The mixed culture 'Chloropseudomonas ethylica' strain 2K has been grown on a medium which enhanced the yield of cytochrome c-551.5 from Desulfuromonas acetoxidans. The cytochrome was purified to homogeneity and an isoelectric point of 8.40 was determined. A determination of the amide content indicated that the cytochrome contains two more amides than previously reported.

Applications of gas-liquid chromatography in protein chemistry. II. Determination of amide residues in nanomolar amounts of proteins

A method for the quantitative determination of amide residues in nanomolar amounts of proteins is described, based on dilute acid hydrolysis at 100 degrees, followed by isothermal gas-liquid chromatography of the ammonia released by on-column neutralisation of the hydrolysate and quantitation by means of a conductometric detector. Amide contents are given for twenty well characterised proteins, as well as for asparagine and glutamine.

The similarity between the primary structures of two non-histone chromosomal proteins

A comparison has been made of two non-histone chromosomal proteins, high-mobility-group proteins 1 and 2. Peptides produced from the two proteins by various chemical and enzymic cleavages have been compared by polyacrylamide gel electrophoresis and peptide mapping. In addition the cysteine content, C-terminal sequences and amide content have been determined for both proteins. The results obtained, together with previous results, show that high-mobility-group proteins 1 and 2 have closely related primary structures, although obviously being different molecules. When analysed by isoelectric focusing both proteins exhibit complex banding patterns. In the case of high-mobility-group protein 1, this could be caused by aggregation, but with high-mobility-group protein 2 there are four distinctive subfractions focusing between pH 7.8 and 8.9.

Properties of two homologous alkaline proteases from Streptomyces rectus

Some physicochemical properties of two thermostable proteases from Streptomyces rectus are described. The enzymes were judged to be identical with respect to molecular weight, inactivation with serine protease inhibitors, and in primary structure by peptide analysis. Amino acid analysis indicated the enzymes had identical compositions except for their amide content. The molecular weights of the enzymes were judged to be 28,000 by sedimentation equilibrium, 26,200 by sedimentation diffusion, and 29,100 from amino acid analysis. Titration of the proteases with diisopropylfluorophosphate and phenylmethane sulfonylfuoride indicate equivalent weights of 28,500 and 32,800 g, respectively, for the proteins. The pentapeptide around the serine residue reacting with diisopropylfluorophosphate was isolated and had the composition: Asx(1), Gly(1), Thr(1), Ser(1), Met(1).

Myxobacter AL-1 protease II: specific peptide bond cleavage on the amino side of lysine

A second extracellular protease from myxobacter strain AL-1 has been purified to homogeneity and named protease II; the enzyme crystallizes as fine needles. The extracellular, cell wall lytic protease reported previously from the same organism is now designated protease I. Protease II exhibits a pH optimum of 8.5 to 9.0 and is stable from pH 3.0 to 9.0. The enzyme is heat stable at 50 C for 18 hr. Results of sedimentation equilibrium studies yielded a molecular weight of 17,000, and amino acid analysis revealed 157 residues with a minimal molecular weight of 16,660. Cleavage of peptide bonds in the oxidized B-chain of insulin, cytochrome c (horse heart). lysozyme, and vasopressin is restricted to the amino side of lysine. Dilysine and trilysine were not hydrolyzed. Products from digestions of polylysine were lysine and dilysine.