A quantitative determination by capillary gas-liquid chromatography of neutral and amino sugars (as O-methyloxime acetates), and a study on hydrolytic conditions for glycoproteins and polysaccharides in order to increase sugar recoveries

Pyridine borane has been reported as a superior reagent over a wide pH range, 5-9, for the reductive methylation of amino groups of proteins with formaldehyde [J. C. Cabacungan , A. I. Ahmed , and R. E. Feeney (1982) Anal. Biochem. 124, 272-278]. It has also been reported to reduce tryptophan to dihydrotryptophan and to inactivate lysozyme in trifluoroacetic acid [M. Kurata , Y. Kikugawa , T. Kuwae , I. Koyama , and T. Takagi (1980) Chem. Pharm . Bull 28, 2274-2275]. In the present study the specificity of pyridine borane for the two different modifications under different reaction conditions has been demonstrated, and extended to the application to the synthesis of protein containing reductively attached carbohydrates. In the acid reduction, pyridine borane selectively reduced all six tryptophans in lysozyme to dihydrotryptophan while all other amino acids remained intact. On similar treatment no cleavage of the carbohydrate moiety from chicken ovomucoid, and no losses of activity of ovomucoid or ribonuclease, two proteins devoid of tryptophan, were observed. Nearly complete methylation of the lysines of lysozyme, chicken ovomucoid, and ribonuclease was achieved with formaldehyde at pH 7.0 after 2 h at room temperature, with the retention of full activity of the protein without any destruction of tryptophan. The same chemistry was applied to covalently attach glucose and lactose to bovine serum albumin. Parameters, including pH, temperature, and methanol, that affect the reactions were investigated. Incremental additions of pyridine borane during the course of the reactions increased the rate of modification. The covalent attachment of sugar to the epsilon-amino group of lysine was demonstrated by the synthesis of N-alpha- acetylglucitollysine and comparison with acid hydrolysates of the bovine serum albumin-sugar derivatives.     

Recovery of tryptophan from 25-minute acid hydrolysates of protein

It was found that thioglycolic acid prevents destruction of tryptophan during rapid hydrolysis of protein with a trifluoroacetic acid/HCl mixture (1:2, v/v) at 166 degrees C for 25 or 50 min. The addition of 5% (v/v) thioglycolic acid gave the maximum tryptophan recovery (88.3%) for a 25-min hydrolysate of lysozyme. Tryptophan recoveries varied slightly among three different proteins; 88% for lysozyme, 73% for alpha-chymotrypsinogen A, and 85% for apomyoglobin. However, when extrapolated to zero time, the values were close to one another: 94, 87, and 88%, respectively. The addition of thioglycolic acid was also advantageous for recovering amino acids other than tryptophan. Particularly, yields of carboxymethylcysteine and methionine were greatly improved. This modified rapid hydrolysis method gave satisfactory results without the need for separate analyses of tryptophan and cysteine, provided proteins were reduced and carboxymethylated prior to hydrolysis.     

Further study on gas phase acid hydrolysis of protein: improvement of recoveries for tryptophan, tyrosine, and methionine

A novel method for vapor phase acid hydrolysis of protein suitable for quantitative analysis of tryptophan is presented. The hydrolysis is carried out in vapor of a mixture made of 7 M HCl, 10% trifluoroacetic acid, and 20% thioglycolic acid in the presence of indole. Reasonably good recoveries of common amino acids, including tryptophan (above 75%), were achieved.     

Complete amino acid analysis of proteins from a single hydrolysate.

An analytical procedure which affords the precise amino acid composition of a protein or a peptide from a single hydrolysate is described. This method utilizes 4 N methanesulfonic acid containing 0.2% 3-(2-aminoethyl)indole, rather then 6N HCl as a catalyst for hydrolysis. The hydrolysis is carried out in vacuo (20 mu) at 115 degrees for 22 to 72 hours. Half-cystine is determined as S-sulfocysteine by treating the hydrolysate with dithiothreitol followed by an excess of tetrathionate. The values of all amino acids, including tryptophan and half-cystine, were close to the expected theoretical values for the proteins examined. The method has the advantage that the neutralized hydrolysate can be applied directly to an ion exchange column. Further, the method is capable of distinguishing between free sulfhydryl groups as S-carbosymethylcysteine and disulfides as S-sulfocysteine. A limitation of the procedure is that tryptophan remains sensitive to the presence of carbohydrate in the sample.     

Determination of methionine sulfoxide in protein and food by hydrolysis with p-toluenesulfonic acid

Methionine sulfoxide in peptides and proteins was determined by use of 3 N p-toluenesulfonic acid as a hydrolyzing agent. Samples were hydrolyzed at 110 degrees C for 22 h in an evacuated sealed tube and analyzed for amino acid content. Amino acid analysis showed that the recovery of methionine sulfoxide from a synthetic peptide and its mixture with proteins was consistently better than 90%. The recovery of all other amino acids except tryptophan was complete, and was similar to that observed after hydrolysis with 6 N HCl. The presence of carbohydrates had no effect on the yield. Thus, the present procedure can be used for general and simultaneous determination of methionine sulfoxide as well as other amino acids in proteins.     

Recovery of tryptophan in peptides and proteins by high-temperature and short-term acid hydrolysis in the presence of phenol

The addition of 3% (w/v) phenol to 6 M HCl largely prevented the destruction of tryptophan during rapid hydrolysis of peptides and proteins at 166 degrees C for 25 min or at 145 degrees C for 4 h. This hydrolysis procedure was advantageous for amino acid microanalysis using conventional high-performance liquid chromatography with a precolumn derivatization technique. The recovery of tryptophan from proteins was at least 80%. The addition of phenol also improved the recovery of methionine and carboxymethylcysteine. The amount of tryptophan in proteins electroblotted onto a polyvinylidene difluoride membrane was determined by this method.     

Studies on Nα-acylated proteins: The N-terminal sequences of two muscle enolases

A standard procedure for the identification of the N-terminal amino acid in N alpha-acylated proteins has been developed. After exhaustive proteolysis, the amino acids with blocked alpha-amino groups are separated from positively charged, free amino acids by ion exchange chromatography and subjected to digestion with acylase I. Amino acid analysis before and after the acylase treatment identifies the blocked N-terminal amino acid. A survey of acylamino acid substrates showed that acylase will liberate all the common amino acids except Asp, Cys or Pro from their N-acetyl-and N-butyryl derivatives, and will also catalyze the hydrolysis of N-formyl-Met and N-myristyl-Val. Thus, the procedure cannot identify acylated Asp, Cys or Pro, nor, because of the ion exchange step, N alpha-acyl-derivatives of Arg, Lys or His. Whenever the protease treatment releases free acylamino acids, the remaining amino acids should be detected. When applied to several proteins, the procedure confirmed known N-terminal acylamino acids and identified acyl-Ser in enolases from chum and coho salmon muscle and in pyruvate kinase from rabbit muscle, and acyl-Thr in phosphofructokinase from rabbit muscle. The protease-acylase assay has been used to identify blocked peptides from CNBr- or protease-treated proteins. When such peptides were treated with 1 N HCl at 110 degrees for 10 min, sufficient yields of deacylated, mostly intact, peptide were obtained to permit direct automatic sequencing. The N-terminal sequences of rabbit muscle and coho salmon enolase were determined in this way and are compared to each other and to the sequence of yeast enolase.     

The direct hydrolysis of proteins containing tryptophan on polyvinylidene difluoride membranes by mercaptoethanesulfonic acid in the vapor phase.

A procedure for the amino acid analysis of polypeptides that contain tryptophan on polyvinylidene difluoride membranes is described. Lysozyme, carbonic anhydrase, phytochrome, and ovalbumin were tested. The protein, which was separated from others by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, was blotted from the gel onto a polyvinylidene difluoride membrane and directly hydrolyzed by 3 N mercaptoethanesulfonic acid vapor in a vacuum at 176 degrees C for 25 min. The hydrolysate was extracted with 0.1 N HCl and 30% methanol and used for amino acid analysis. The tested proteins were adequately hydrolyzed, and the recovery of tryptophan was very efficient.     

A new acid hydrolysis method for determining tryptophan in peptides and proteins

Three different methods for hydrolysis and determination of amino acid composition of peptides and proteins were compared. We found, that the method of Matsubara and Sasaki (using 6N HCl and thioglycolic acid) gives comparatively low recoveries for tryptophan, while Liu and Chang's method, using p-toluenesulfonic acid and tryptamine, is more suitable. To eliminate the difficulties of the latter method, we used mercaptoethane-sulfonic acid, which, in the concentration used, results in total hydrolysis of peptide bonds within 22 hr and gives very high tryptophan recoveries. Both sulfonic acid methods were used for hydrolysis of the pentapeptide “pentagastrine” as well as of the proteins lysozyme, cytochrome c, and chymotrypsine. Their amino acid composition was determined using an automatic amino acid analyzer. Similarly to the p-toluenesulfonic acid method, the results of our method are totally reliable only for pure peptides and proteins, though the results obtained with our method using samples containing carbohydrates are better than those of all earlier methods.     

Acid hydrolysis of protein in a microcapillary tube for the recovery of tryptophan

The acid hydrolysis of proteins was miniaturized and simplified by employing microcapillary tubes (100 microl in volume) with 6 M HCl containing 1% 2-mercaptoethanol and 3% phenol for an amino acid compositional analysis. The method not only eliminated the laborious evacuation step for the hydrolysis tube but also decreased the destruction of tryptophan during hydrolysis. The recovery of tryptophan was 79% by acid hydrolysis at 145 degrees C for 4 h. Since the acid mixture could be removed under vacuum, the hydrolysate was subjected to an amino acid analysis without neutralization or dilution.     

Reactions of hydroxyamino acids during hydrochloric acid hydrolysis

Chlorosubstitution reactions occur readily during HCl hydrolysis of delta- and epsilon-hydroxynorleucines (Hnle), the products of deamination of poly-L-lysine by nitrite at low pH. During amino acid analysis, chloronorleucines elute as new peaks after delta- and epsilon-Hnle. To determine if other hydroxyamino acids undergo similar changes during hydrolysis, they were subjected individually to HCl hydrolysis conditions with and without added phenol. Amino acid analyses indicated that terminal hydroxy groups on linear side chains undergo reactions during HCl hydrolysis; the products appear as new peaks which may be chloroderivatives. In contrast, no new peaks are observed in HCl hydrolysates of delta-hydroxylysine or amino acids with beta-hydroxy groups (beta-hydroxynorvaline, serine, and threonine). Phenol did not protect linear amino acids from reactions during HCl hydrolysis but did prevent loss of the cyclic amino acids tyrosine, hydroxyproline, and 3,4-dihydroxyphenylalanine. Although the gamma-hydroxy group of homoserine would be expected to undergo reaction, HCl catalyzes its cyclization to form homoserine lactone instead.     

A new double-labelling procedure for determination of amino acid composition: application to bacteriorhodopsin

A new double-labelling procedure for amino acid analysis which requires only routine chromatographic equipment is described. When 1-fluoro-2,4-dinitro[3H]benzene is reacted with a mixture of 14C-labelled amino acids followed by reaction with the same 14C-labelled amino acid mixture diluted with an unlabelled sample of amino acids, the 3H:14C ratio in the resulting 2,4-dinitrophenyl (DNP) amino acid derivatives of the diluted sample will be increased in proportion to the quantity of unlabelled amino acid in the diluted sample. This procedure gave reliable results when applied to the known proteins insulin and lysozyme. The procedure is most advantageous when applied to amino acids which are unstable during acid hydrolysis or present in low molar fractions. When applied to the analysis of the bacteriorhodopsin in Halobacterium cutirubrum, this procedure showed the presence of one histidine residue and four tryptophan residues per mole protein but no cystine or cysteine; in general, the analyses obtained were consistent with those originally reported by Oesterhelt, D. and Stoeckenius, W. (1971) (Nature (London) New Biol. 233, 149-152) for bacteriorhodopsin of H. halobium.     

Amino acid analysis on polyvinylidene difluoride membranes

A procedure for the amino acid analysis of proteins electrotransferred to polyvinylidene difluoride (PVDF) membranes is described. The proteins are first separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and then electroblotted onto a PVDF membrane. After staining with Coomassie brilliant blue, the visualized protein bands are excised from the membrane. Each band is placed in a vial and subjected to gas-phase hydrolysis in 6 N HCl in a vacuum desiccator at 110 degrees C. The amino acids are extracted from the membrane into 0.1 N HCl/30% CH3OH and analyzed by reverse-phase HPLC using postcolumn o-phthalaldehyde-derivatizing reagent. The method was shown to give reproducible and reasonably accurate compositions for several proteins, as well as to provide an estimate of protein content. As little as 10 pmol of a 67-kDa protein can be determined.     

Specific sulfonation of tyrosine, tryptophan and hydroxy-amino acids in peptides

1. ClSO3H in trifluoroacetic acid rapidly converts serine and threonine into O-sulfate ester derivatives while tyrosine and tryptophan are converted into arylsulfonic acids. 2. H2SO4 in trifluoroacetic acid reacts more slowly with serine, threonine and tyrosine while is not able to modify tryptophan. 3. All other amino acids are perfectly stable under the above reaction conditions. 4. Peptides containing susceptible amino acid residues are specifically converted into the corresponding sulfonated derivatives in high or quantitative yield.     

A rapid vapor-phase acid (hydrochloric acid and trifluoroacetic acid) hydrolysis of peptide and protein

A new method for the acid hydrolysis of protein is presented. Peptide bonds are cleaved by the action of an HCl/trifluoroacetic acid (TFA) vapor mixture. Contamination for the hydrolysis mixture is reduced to low levels (1-3 pmol). Recovery of hydrophobic amino acid is improved. Short reaction times are achieved and rapid removal of acids is facilitated. The reaction temperature is 158 degrees C for reaction times of 22.5 and 45 min with 7 M HCl and 10% TFA containing 0.1% phenol.     

A rapid microdetermination of phosphoserine, phosphothreonine, and phosphotyrosine in proteins by automatic cation exchange on a conventional amino acid analyzer

A cation-exchange chromatographic method for the separation and determination of phosphoserine, phosphothreonine, and phosphotyrosine in proteins after partial acid hydrolysis is described. The short column (0.6 X 8 cm) of an automatic amino acid analyzer was used and elution was carried out isocratically with 10 mM trifluoroacetic acid. The method is highly sensitive and each of the three O-phosphoamino acids can be accurately determined down to the 50-pmol level. Higher sensitivity may be obtained by the use of [32P]phosphate-labeled proteins. A correction factor for the decomposition of phosphoserine or phosphothreonine during acid hydrolysis can be deduced from the amount of inorganic phosphate recovered at the column void volume. The method is sensitive enough to be used for 32P-labeled proteins isolated by two-dimensional gel electrophoresis.     

Analysis of adipimidate-crosslinked lysine

The chromatographic conditions for separation of N,N′-bislysyl(?-N)adipamidine and N-lysyl(?-N)adipamidinic acid, which were the products of acid hydrolysis of proteins treated with adipimidate esters, from other amino acids on an amino acid analyzer were established including their ninhydrin color values. Kinetics of decomposition of these lysine derivatives under the conditions of total acid hydrolysis of protein are also reported.     

The preparation of matrix-bound proteases and their use in the hydrolysis of proteins

Four proteases, crude acid protease from Aspergillus, pronase, amino-peptidase M, and prolidase, have been covalently attached to activated agarose and to amino propyl glass beads. The matrix-bound enzymes have been tested as catalysts for the complete hydrolysis of protein substrates, with the primary goal to isolate unstable amino acid derivatives present in the substrate protein. Under conditions used in the present work, the total amino acid release from the protease-catalyzed hydrolysis of four substrate proteins (pancreatic ribonuclease, egg white lysozyme, yeast enolase, and bovine insulin) was 95–103% of that observed in standard acid hydrolysis. Recovery of individual amino acids showed greater deviation from the theoretical values, but cystine was the only amino acid recovered in low yields (42–77%) from all four proteins. Derivatized amino acids, such as methionine sulfoxide, O-(butylcarbamoyl)-serine, and N-glycosyl asparagine have been obtained from chemically modified proteins or from unmodified glycoprotein in good yield, and normal amino acid constituents of proteins which cannot be quantified after acid hydrolysis (tryptophan, asparagine, and glutamine) have also been determined either directly after proteolysis or after proteolysis in conjunction with acid hydrolysis.     

Amine boranes as alternative reducing agents for reductive alkylation of proteins

The use of several commercially available amine-borane complexes was investigated for the reductive methylation of amino groups of several proteins. An earlier study in our laboratory, using turkey ovomucoid as the model protein, showed that dimethylamine borane is a slightly weaker reducing agent, but a good, less toxic substitute for sodium cyanoborohydride (K. F. Geoghegan, J. C. Cabacungan, H. B. F. Dixon, and R. E. Feeney, 1981, Int. J. Peptide Protein Res.17, 345–352). N-α-Acetyl-l-lysine, poly-l-lysine, turkey ovomucoid, bovine serum albumin, chicken ovalbumin, β-lactoglobulin, casein, and soybean protein were reductively methylated with dimethylamine borane and trimethylamine borane. The latter produced a consistently lower degree of modification even in the presence of sodium dodecyl sulfate. In a comparison that included the boranes triethylamine, t-butylamine, morpholine, and pyridine, pyridine borane was found to be slightly stronger than sodium cyanoborohydride. In a pH 7 solution containing 2 mmN-α-acetyl-l-lysine and 20 mm formaldehyde, complete dimethylation was achieved with about 10 mm pyridine borane after 2 h incubation at 22°C, while more than 15 mm was necessary with sodium cyanoborohydride. Like dimethylamine borane, both pyridine borane and triethylamine borane showed a reducing capacity at pH 7 which was as high as that at pH 9. Reductive alkylation under neutral to mild acid conditions allows modification of alkaline labile proteins and also limits the side reactions between proteins and formaldehyde.     

Fermentation of acid hydrolysates from olive-tree pruning debris by Pachysolen tannophilus

The influence of the type and concentration of acid in the hydrolysis process and its effect on the subsequent fermentation by Pachysolen tannophilus (ATCC 32691) to produce ethanol and xylitol was studied. The hydrolysis experiments were performed using hydrochloric, sulphuric and trifluoroacetic acids in concentrations ranging from 0.1 to 1.0 N, a temperature of 90 degrees C, and a time of 240 min. The fermentation experiments were conducted on a laboratory scale in a batch-culture reactor at pH 4.5 and 30 degrees C. The hydrolysis with the highest acid concentration produced the complete solubilization of hemicellulose to monosaccharides. The highest values for the specific rate of ethanol production were registered in cultures hydrolyzed with trifluoroacetic acid, and values were found to decrease as the acid concentration increased. The highest values of overall ethanol yields ( [Formula: see text] = 0.37 kg kg(-1)) were also found in the fermentation of the hydrolysates of trifluoroacetic acid.