[Separation of phenylalanine and methionine enantiomers by HPLC method: a comparison of stationary phase types]

The paper deals with enantioselective separation of amino acids by the high performance liquid chromatography method. Separations of enantiomeric forms were tested on the chiral stationary phases based on β-cyclodextrine, isopropyl carbamate cyclofructan 6, and the macrocyclic antibiotic teicoplanin. The best enantioseparation was obtained on the teicoplanin-based chiral stationary phase in the reversed-phase mode. UV spectrophotometric detection at 210 nm was used for detection of amino acids. The method was validated with respect to linearity, precision, limit of detection, limit of quantitation, and recovery. Limits of quantitation for phenylalanine and methionine enantiomers were 0.3 and 0.2 µg.ml-1, respectively. The HPLC method with teicoplanin-based chiral stationary phase was applied for analysis of dietary supplements.Key words: separation of enantiomers HPLC phenylalanine methionine.

Penilumamide, a novel lumazine peptide isolated from the marine-derived fungus, Penicillium sp. CNL-338

A novel lumazine peptide, penilumamide (1), was isolated from the fermentation broth of a marine-derived fungal strain, identified as Penicillium sp. (strain CNL-338) and the structure of the new metabolite was determined by analysis of ESI-TOF MS data combined with 1D and 2D NMR experiments.

Adsorption behavior of a teicoplanin aglycone bonded stationary phase under harsh overload conditions

Silica-bonded teicoplanin aglycone allows enantioseparation of amino acids by reversed-phase liquid chromatography with a low organic solvent content. However, a reversible change in the adsorption behavior leading to a retention time shift (RTS) was observed when a preparative scale column was treated with harsh preparative chromatography-like conditions between finite-injection HPLC runs conducted under exactly the same conditions. This behavior was observed for all five investigated aliphatic and aromatic amino acids. In all cases, the retention times were prolonged after the overload conditions and the RTS was more pronounced for the later eluting d-enantiomer. We defined a standardized method for measuring the RTS and performed a systematic investigation on the influence of experimental conditions (type and concentration of pH modifier and organic modifier, temperature, pH) on the RTS. In this way a solvent composition--90/10 50 mM NH4Ac pH 5.8/MeOH--was identified that yielded no observable shift in retention time after overload conditions for both enantiomers. In order to treat the observed phenomenon on a mechanistic level, we applied band profile analysis based on the stochastic theory of chromatography and identified two different enantioselective sites. When the band profile analysis was performed on elution profiles obtained from runs with prolonged retention time after harsh overload conditions, the retention time shift could be attributed to both differentiable types of adsorption sites. One site was found to make both, enantioselective and non-selective contributions.

Application of an eremomycin-chiral stationary phase for the separation of DL-methionine using simulated moving bed technology

Recently a new chiral stationary phase (CSP) was introduced, based on the immobilization of the macrocyclic glycopeptide eremomycin to epoxy-activated silica. The application of this new CSP to preparative enantioseparation using simulated moving bed (SMB) chromatography will be presented. MeOH-H(2)O (0.1M NaH(2)PO(4))=20/80 (v/v) was used as the mobile phase to separate the enantiomers of methionine. Successful separation was realized providing productivities around 15 g(product)/l(stat)/h for both l and d-methionine under nonlinear conditions. In such delicate continuous chromatographic separation processes, besides productivity, the long-term stability of the applied stationary phases is of importance. Column to column fluctuations were negligible and long-term stability of the preparative stationary phase was satisfactory according to the results of perturbation experiments performed before and after long-term SMB runs.

Analysis of methionine oxides and nitrogen-transporting amino acids in chilled and acclimated maize seedlings

In maize seedlings, chilling causes a reduction of glutamine synthetase (GS) activity, while acclimation protects GS (manuscript submitted). Since ROS can oxidize both protein-bound and free Met to methionine sulfoxide (MSO) and further to methionine sulfone (MSO2, a GS inhibitor), it was hypothesized that the chilling-induced oxidative stress may cause accumulation of MSO and MSO2, thus contributing to the inactivation of GS. MSO2 preferentially inhibited the chloroplastic isoform, GS2. HPLC analysis of polar amino acids from coleoptiles + leaves, mesocotyls and roots of control, chilled, acclimated, acclimated and chilled and chilled and rewarmed plants revealed that free MSO and MSO2 do not accumulate after low temperature treatments. Nevertheless, acclimation significantly increased the expression of putative protein methionine sulfoxide reductase (PMSR), especially in mesocotyls. Different low temperature treatments caused complex changes in the profiles of N-transporting amino acids, Asp, Glu, Asn and Gln.

Cycling of volatile organic sulfur compounds in anaerobically digested biosolids and its implications for odors

The objectives of this research were to elucidate the mechanisms for production and degradation of volatile organic sulfur compounds (VOSCs), key odor causing compounds produced by biosolids. These compounds included methanethiol (MT), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS). A series of experiments were used to probe various pathways hypothesized to produce and degrade these VOSCs. The production of MT was found to mainly occur from degradation of methionine and the methylation of hydrogen sulfide. DMS was formed through the methylation of MT. DMDS was formed by MT oxidation. All three of the VOSCs were readily degraded by methanogens and a cyclic pathway was proposed to describe the production and degradation of VOSCs. The research demonstrated that the main source of VOSCs was the biodegradation of protein within the biosolids and the results provided a framework for understanding the production of odor from anaerobically digested sludges before and after dewatering.

Methionine production by fermentation

Fermentation processes have been developed for producing most of the essential amino acids. Methionine is one exception. Although microbial production of methionine has been attempted, no commercial bioproduction exists. Here, we discuss the prospects of producing methionine by fermentation. A detailed account is given of methionine biosynthesis and its regulation in some potential producer microorganisms. Problems associated with isolation of methionine overproducing strains are discussed. Approaches to selecting microorganism having relaxed and complex regulatory control mechanisms for methionine biosynthesis are examined. The importance of fermentation media composition and culture conditions for methionine production is assessed and methods for recovering methionine from fermentation broth are considered.

An ionizable chromophoric reagent for the analysis of primary amine-containing drugs by capillary electrophoresis

We found that ofloxacin acyl chloride is a potential chromophoric reagent for labeling amino analytes for capillary electrophoresis. Ofloxacin acyl chloride has a tertiary amino function in its structure and the derivatives from ofloxacin acyl chloride reacting with amino analytes can be ionized by an acid treatment and analyzed by simple capillary zone electrophoresis. Ofloxacin acyl chloride was used to derivatize model analytes (without chromophore) of amantadine (amino drug), tranexamic acid (non-protein amino carboxylic acid), glycine, and methionine (protein amino acids). The resulting derivatives were analyzed by capillary zone electrophoresis with ultraviolet detection (300 nm). The detection limits of the analytes studied were in the range of 1.0-2.5 microM (S/N = 3, injection 3 s). The precision (relative standard deviation) and accuracy (relative error) of the method for intra- and inter-day analyses of the analytes were respectively below 4.5% and 3.9%. Application of the method to the analysis of tranexamic acid in plasma proved feasible.

Fully automated synthesis module for preparation of S-(2-[(18)F]fluoroethyl)-L-methionine by direct nucleophilic exchange on a quaternary 4-aminopyridinium resin

A fully automated preparation of S-(2-[(18)F]fluoroethyl)-L-methionine (FEMET), an amino acid tracer for tumor imaging with positron emission tomography, is described. [(18)F]F(-) was produced via nuclear reaction (18)O(p,n) [(18)F] at PETtrace Cyclotron. Direction nucleophilic fluorination reaction of [(18)F]fluoride with 1,2-di(4-methylphenylsulfonyloxy)ethane on a quaternary 4-(4-methylpiperidinyl)pyridinium functionalized polystyrene anion exchange resin gave 2-[(18)F]-1-(4-methylphenyl-sulfonyloxy)ethane, and then [(18)F]fluoroalkylation of L-homocysteine thiolactone with 2-[(18)F]-1-(4-methylphenylsulfonyloxy)ethane yielded FEMET. The overall radiochemical yield with no decay correction was about 10%, the whole synthesis time was about 52 min, and the radiochemical purity was above 95%.

Inventory and functional characterization of the HAK potassium transporters of rice

Plants take up large amounts of K(+) from the soil solution and distribute it to the cells of all organs, where it fulfills important physiological functions. Transport of K(+) from the soil solution to its final destination is mediated by channels and transporters. To better understand K(+) movements in plants, we intended to characterize the function of the large KT-HAK-KUP family of transporters in rice (Oryza sativa cv Nipponbare). By searching in databases and cDNA cloning, we have identified 17 genes (OsHAK1-17) encoding transporters of this family and obtained evidence of the existence of other two genes. Phylogenetic analysis of the encoded transporters reveals a great diversity among them, and three distant transporters, OsHAK1, OsHAK7, and OsHAK10, were expressed in yeast (Saccharomyces cerevisiae) and bacterial mutants to determine their functions. The three transporters mediate K(+) influxes or effluxes, depending on the conditions of the experiment. A comparative kinetic analysis of HAK-mediated K(+) influx in yeast and in roots of K(+)-starved rice seedlings demonstrated the involvement of HAK transporters in root K(+) uptake. We discuss that all HAK transporters may mediate K(+) transport, but probably not only in the plasma membrane. Transient expression of the OsHAK10-green fluorescent protein fusion protein in living onion epidermal cells targeted this protein to the tonoplast.

Immobilization of an L-aminoacylase-producing strain of Aspergillus oryzae into gelatin pellets and its application in the resolution of D,L-methionine

The conditions for immobilization of an l-aminoacylase-producing strain of Aspergillus oryzae in gelatin and the enzymic characteristics of the immobilized pellets were studied. The optimal concentrations of gelatin, glutaraldehyde and ethyldiamine and time of immobilization were determined. Scanning electron micrographs reveal the cross-linked structure differences between the native and immobilized pellets. Optimum pH and temperature of the native and immobilized pellets were determined. Effects of ionic strength and substrate concentration on relative activity of the native and immobilized pellets were investigated in detail. The immobilized pellets were more stable over broader temperature and pH ranges. In addition, the immobilized pellets showed stable activity under operational and storage conditions. The immobilized pellets lost about 20% of their initial activity after five cycles of reuse. The results reported in this paper show the potential for using the immobilized A. oryzae pellets to resolve d,l-methionine.

Resolution of enantiomers of DL-amino acids on silica gel plates impregnated with optically pure (-)-quinine

TLC resolution of enantiomers from racemic amino acids was achieved on silica gel plates impregnated with optically pure (-)-quinine. The successful solvent systems were butanol-chloroform-acetic acid (3:7:5, v/v) for DL-methionine; 6:8:4, v/v for alanine; 10:1:4; v/v for threonine; and ethyl acetate-carbon tetrachloride-propionic acid (10.5:6.5:3.5, v/v) for valine. Minimum detection limits were found to be different for each of the amino acid, ranging between 0.9 and 3.7 microg. The effects of concentration of impregnating reagent, temperature and pH on resolution of enantiomers have been studied in details.

High conversion in asymmetric hydrolysis during permeation through enzyme-multilayered porous hollow-fiber membranes

We describe a novel porous hollow-fiber support for immobilizing aminoacylase in multilayers. Epoxy-group-containing polymer chains were grafted onto a porous hollow-fiber membrane by radiation-induced graft polymerization of glycidyl methacrylate, and subsequently a diethylamino group as an anion-exchange group was introduced into the graft chain. Aminoacylase was adsorbed in multilayers by allowing the amioacylase buffer solution to permeate through the pores across the hollow fiber; the graft chains provided three-dimensional space for the enzymes because of their electrostatic repulsion. The adsorbed enzyme at a degree of multilayer binding of 15 was cross-linked with glutaraldehyde to prevent leakage. An acetyl-DL-methionine solution was allowed to permeate through the pores surrounded by the aminoacylase-immobilized graft chain. Production of L-methionine was observed at a 4.1 mol/h per L of the fiber for a space velocity of 200 h(-1), defined as the flow rate of the effluent penetrating the outside surface of the hollow fiber divided by the membrane volume including the lumen.

Analysis of L-[methyl-11C]methionine and metabolites in human plasma by an automated solid-phase extraction and a high-performance liquid chromatographic procedure

A fully automated method for separation of L-[methyl-11C]Methionine from metabolites in patient plasma was developed. L-[methyl-11C]Methionine was isolated from plasma by solid-phase extraction (SPE). The radioactivity retained on the SPE column was eluted and injected onto the HPLC system for separation of in vivo formed L-[methyl-11C]methionine radiolabeled metabolites. The yield through the isolation procedure and HPLC analysis was greater than 95% with a precision better than 5% (R.S.D.). The calculated rate of L-[methyl-11C]methionine transport into tumor tissue was markedly different with and without compensation for radiolabeled metabolites in patient plasma.

The methionine salvage pathway in Klebsiella pneumoniae and rat liver. Identification and characterization of two novel dioxygenases

The 5-methylthio-D-ribose moiety of 5'-(methylthio)-adenosine is converted to methionine in a wide variety of organisms. 1,2-Dihydroxy-3-keto-5-methylthiopentene anion (an aci-reductone) is an advanced intermediate in the methionine salvage pathway present in the Gram-negative bacterium Klebsiella pneumoniae and rat liver. This metabolite is oxidized spontaneously in air to formate and 2-keto-4-methylthiobutyric acid (the alpha-keto acid precursor of methionine). Previously, we had purified an enzyme (E2) from Klebsiella which catalyzes the oxidative degradation of the aci-reductone to formate, CO, and methylthiopropionic acid. To further characterize the reactions of the aci-reductone we used its desthio analog, 1-2-dihydroxy-3-ketohexene anion (III), which was described previously. This molecule undergoes the analogous enzymatic and non-enzymatic reactions of the natural substrate, namely the formation of formate, CO, and butyrate from III. Experiments with 18O2 show that E2 is a dioxygenase which incorporates one molecule of 18O into formate and butyric acid. No cofactor has been identified. We were unable to find an enzyme which catalyzes the conversion of 1,2-dihydroxy-3-keto-5-methylthiopentane to a keto acid precursor of methionine. The keto acid is probably produced non-enzymically in Klebsiella. We have, however, identified and purified an enzyme (E3) from rat liver, which catalyzes the formation of formate and 2-oxopentanoic acid from III. This enzyme has a monomeric molecular mass of 28,000 daltons, and no chromophoric cofactor has been identified. Experiments with 18O2 show that E3 is a dioxygenase which incorporates an 18O molecule into formate and the alpha-keto acid. In rat liver CO formation was not detected.

[Use of analogs of primary metabolites in the selection of the producer of polymyxin B]

A number of amino acids were found to have effects on the growth of the polymyxin B-producing culture and biosynthesis of the antibiotic by it. Of special importance was the stimulating effect by methionine. Four selection stages were carried out with using structural analogs of purines and amino acids as selective factors. There were no stable variants with increased antibiotic productivity among the mutants resistant to the analogs of purines and leucine. The levels of polymyxin B accumulation by the variants resistant to 4-fluorophenylalanine were 30 to 50 per cent higher than those in the controls and the variants were characterized by low morphological and antibiotic production variation in the subcultures. The mechanisms of the methionine physiological effect and the prospects of using analogs of the primary metabolites in improvement of the culture producing polymyxin B are discussed.

Betaine:homocysteine methyltransferase--a new assay for the liver enzyme and its absence from human skin fibroblasts and peripheral blood lymphocytes

Chronic elevation of plasma homocysteine is associated with increased atherogenesis and thrombosis, and can be lowered by betaine (N,N,N-trimethylglycine) treatment which is thought to stimulate activity of the enzyme betaine:homocysteine methyltransferase. We have developed a new assay for this enzyme, in which the products of the enzyme-catalysed reaction between betaine and homocysteine are oxidised by performic acid before being separated and quantified by amino acid analysis. This assay confirmed that human liver contains abundant betaine:homocysteine methyltransferase (33.4 nmol/h/mg protein at 37 degrees C, pH 7.4). Chicken and lamb livers also contain the enzyme, with respective activities of 50.4 and 6.2 nmol/h/mg protein. However, phytohaemagglutinin-stimulated human peripheral blood lymphocytes and cultured human skin fibroblasts contained no detectable betaine:homocysteine methyltransferase (less than 1.4 nmol/h/mg protein), even after cells were pre-cultured in media designed to stimulate production of the enzyme. The results emphasize the importance of the liver in mediating the lowering of elevated circulating homocysteine by betaine.

Buffer solutes as stabilizers of 35S-amino acids: a study of volatility, radiochemical purity and biological activity

It is well established that volatile radioactive compounds are associated with preparations of 35S-amino acids, but misconceptions still exist. The addition of stabilizers to these preparations has created a false sense of security regarding the evolution of these volatiles from cell culture medium. Experiments presented here show that the commercially used buffers L-lysine, tricine and 3,4-pyridine-dicarboxylic acid all reduced, but did not eliminate, the evolution of 35S volatiles from tissue culture medium. In each case, the rate of release was approximately 12 nCi/mCi/day (or 0.001%), compared to approximately 44 nCi/mCi/day in the buffer's absence. None of six alternative buffers tested are more effective than the commercially used buffers. We found that the release of labeled volatiles is dependent on the nature of the culture medium, but is no greater from crude 35S-amino acid preparations than from purified 35S-methionine. These commercially used buffers are also effective in maintaining radiochemical purity and are compatible with biological activity; however, because these buffers do not entirely eliminate the release of radioactivity into the gas phase, routine safe-handling procedures should be practiced when working with these products.

Measles virus hemagglutinin. Removal of the initiator methionine in the mature protein, and evidence for further processing to produce a 'ragged' end

Measles virus hemagglutinin has been isolated by immunoadsorption. The total composition of the protein and its N-terminal amino acid sequence give data matching the structure indirectly deduced from cDNA. However, direct analysis of the hemagglutinin also shows that the mature protein is proteolytically processed and has a partly heterogeneous N-terminus. The initiator Met is removed, and non-stoichiometrically also the second residue.

N2-(1-carboxyethyl)methionine. A 'pseudo-opine' in octopine-type crown-gall tumours

A novel methionine-containing plasmid-determined compound, N2-(1-carboxyethyl)methionine (NCEM) has been identified in crown-gall tumours induced by octopine-type strains of Agrobacterium tumefaciens. NCEM is probably synthesized by octopine synthase. Cell-free preparations from octopine-type strains of A. tumefaciens can degrade NCEM; however, the bacterium cannot transport the compound into the cell, although these strains can take up and degrade the octopine family of opines.

Purification and characterization of some metabolic effects of S-neplanocylmethionine

Our laboratory has previously demonstrated that treatment of mouse L929 cells with 1 microM neplanocin A results in the metabolic formation of S-neplanocylmethionine (Keller, B.T., and R.T. Borchardt, Biochem. Biophys. Res. Commun. 120:131-137 (1984]. The present study describes an efficient procedure for the purification of this analog from L cells based on its inherent chemical stability in alkaline conditions. Several metabolic effects of S-neplanocylmethionine are also reported. In L cells, S-neplanocylmethionine was determined to have an apparent half-life of 13 hr compared to 1 hr for S-adenosylmethionine during the initial 2 hr of a cycloleucine block. Analysis of polyamine levels in neplanocin A-treated cells showed a 3.8-fold decrease in putrescine and a 1.7-fold decrease in spermidine by 24 hr, reflecting a decrease in the cell growth rate in response to neplanocin A rather than a direct effect of S-neplanocylmethionine on the cellular S-adenosylmethionine decarboxylase. Consistent with these results are our findings that S-neplanocylmethionine does not significantly inhibit purified rat prostate or Escherichia coli S-adenosylmethionine decarboxylase and that [carboxy-14C]S-neplanocylmethionine exhibits no substrate activity with either enzyme. Purified S-neplanocylmethionine was observed to be a weak inhibitor of both S-adenosylmethionine-dependent protein carboxymethyltransferase and lipid methyltransferase in L cell extracts, having an IC50 value of 205 microM (S-adenosylmethionine = 10 microM). Similar studies with [methyl-3H]S-neplanocylmethionine indicate that the analog has little substrate activity in these two L cell methylation reactions and thus appears to act as a poor competitive inhibitor.

Radioactive methionine: determination, and distribution of radioactivity in the sulfur, methyl and 4-carbon moieties

A simple and inexpensive method is described for isolation and determination of [14C]methionine in the non-protein fraction of tissues extensively labeled with 14C. The effectiveness of the method was demonstrated by isolation of non-protein [14C]methionine (as the carboxymethylsulfonium salt) of proven radiopurity from the plant Lemna which had been grown for a number of generations on [U-14C]sucrose and contained a 2000-fold excess of 14C in undefined non-protein compounds. To our knowledge, this is the first reported assay for radioactive methionine under these demanding conditions. This method also offers an attractive alternative to the use of more expensive and sophisticated equipment for assay of radioactive methionine under less demanding conditions. An advantage is that the isolated methioninecarboxymethylsulfonium salt is readily degraded to permit separate determination of radioactivity in the 4-carbon, methyl and sulfur moieties of methionine. During this work, a facile labilization of 3H attached to the (carboxy)methylene carbon of methioninecarboxymethylsulfonium salt was observed. This labilization is ascribed to formation of a sulfur ylid.

Sodium sulfite as an antioxidant in the acid hydrolysis of bovine pancreatic ribonuclease A

Treatment of hydrochloric acid with sodium sulfite prior to the acid hydrolysis of bovine pancreatic ribonuclease A has been found to suppress the oxidation of cystine, methionine, and tyrosine without adversely affecting the recoveries of other amino acids. Statistical analysis of the results indicated that the assumption of the independence of the mean and the variance, an assumption commonly used in the evaluation of the effects of various treatments, may not be valid in evaluating antioxidants used in the acid hydrolysis of proteins.

Storage protein precursor polypeptides in cotyledons of Pisum sativum L. Identification of, and isolation of a cDNA clone for, an 80000-Mr legumin-related polypeptide

An 80 000-Mr polypeptide, which bound to anti-legumin IgG, was detected among labelled polypeptides from cotyledons at late stages of development. When poly(A)-containing RNA from similar cotyledons was translated in a cell-free protein-synthesizing system, an 80 000-Mr polypeptide was also detected. Immunoprecipitation of translation products with anti-legumin IgG showed that, in addition to the major legumin precursor polypeptides of Mr approximately 60 000, the 80 000-Mr polypeptide was specifically immunoprecipitated. A cDNA clone, pCD32, was found to select an RNA coding for an 80 000-Mr polypeptide in hybrid-selection experiments. Additional minor polypeptides of Mr 63 000 and 65 000 were present in translation products of RNA selected by pCD32; all three polypeptides were immunoprecipitated by anti-legumin IgG. Thermal elution of RNAs bound to pCD32 showed that the affinity of pCD32 to the RNA coding for the 80 000-Mr polypeptide was greater than to the RNAs coding for the 63 000-Mr and 65 000-Mr polypeptides. In similar hybrid-selection experiments, another cDNA clone, pCD40, selected RNAs coding predominantly for polypeptides of Mr 63 000 and 65 000. A minor polypeptide of Mr 80 000 was also detected among these products; again all three polypeptides were immunoprecipitated by anti-legumin IgG. Peptide mapping revealed close similarities between the 80000-Mr polypeptide and the 63 000-Mr/65 000-Mr polypeptides obtained by translation of RNAs selected by pCD32. There were similarities also between maps obtained from translation products of RNA selected by pCD32 and those obtained from anti-legumin IgG immunoprecipitates of total translation products of poly(A)-containing RNA.

Identification of 2-keto-4-methylthiobutyrate as an intermediate compound in methionine synthesis from 5'-methylthioadenosine

The synthesis of methionine from 5'-methylthioadenosine was examined in vitro using cell-free homogenates of rat liver. We had previously reported that methionine synthesized by this system contained carbons from the ribose moiety of 5'-methylthioadenosine (Backlund, P. S., Jr., and Smith, R. A. (1981) J. Biol. Chem. 256, 1533-1535). The present study examines some of the steps involved in this conversion. 2-Keto-4-methylthiobutyrate was identified as one of the products of 5'-[methyl]14C]methylthioadenosine when incubated in vitro with rat liver homogenates. Partial purification of the enzyme system by gel exclusion chromatography to remove small molecular weight substrates and cofactors revealed that synthesis of 2-keto-4-methylthiobutyrate requires magnesium and is inhibited by calcium. 5-Methylthioribose 1-phosphate can replace 5'-methylthioadenosine as a substrate for methionine synthesis under these conditions, but 5-methylthioribose cannot. 5-Methylthioribonic acid was prepared and was found not to be an intermediate compound in this pathway. The final step in this pathway for methionine synthesis is then the transamination of the keto acid, catalyzed by glutamine and asparagine transaminases.

Methionine sulfoxide in the resilium protein of surf clams

A high content of methionine sulfoxide was observed in the resiliums (internal hingeligaments) of surf clams. As no isolation procedure which might cause the oxidation of methionine to methionine sulfoxide was involved and the hydrolysis was carried out in vacuo, it is the first solid evidence for the presence of methionine sulfoxide as a constituent of natural protein.

[35S]-methionine labelled polypeptides from HELA cells. Coordinates and percentage of some major polypeptides

A total of 1169 [35S]-methionine labelled polypeptides (855-acidic (IEF) and 314 basic (NEPHGE) from 100 asynchronous human HeLa cells have been separated using high resolution two dimensional gel electrophoresis. Beside numbering these spots, we give for the major polypeptides their coordinates (M.W. and relative mobility respect to beta-actin (IEF) or NEPHGE), and percentage of total protein label. A few major polypeptides have been identified.

The N-terminal residue of bovine rhodopsin is acetylmethionine

By affinity chromatography on a concanavalin A-Sepharose column and gel filtration on a Sephadex G-25 column, a glycopeptide of 16 amino acid residues has been separated from a tryptic digest of reduced and carboxymethylated bovine rhodopsin. The glycopeptide was treated with cyanogen bromide and products were subjected to high-voltage paper electrophoresis. N-Blocked homoserine separated was reacted first with anhydrous hydrazine and then with dansyl chloride. The product was identified by thin-layer chromatography to be 1-acetyl-2-dansyl hydrazine, thus showing that the N-terminal blocking group was an acetyl group. The remaining peptide after cyanogen bromide treatment was partially sequenced by the Edman dansylation method. The present results and previously reported findings on the binding site of the sugar moiety, taken together, indicate that the N-terminal heptapeptide has the following structure: acetylMet-Asn(carbohydrate)-Gly-Thr-Glx-Gly-Pro.

Amino-acid sequence of dihydrofolate reductase from a methotrexate-resistant mutant of Streptococcus faecium and identification of methionine residues at the inhibitor binding site

The amino-acid sequence of dihydrofolate reductase (7,8-dihydrofolate:NADP(+) oxidoreductase, EC 1.5.1.4) from S. faecium var Durans strain A is reported, and methionine residues 28 and 50 are shown to be protected by the inhibitor aminopterin from carboxymethylation by iodoacetate which occurs in absence of the inhibitor. Comparison of the sequence with that of the Escherichia coli reductase reveals two domains of considerable homology, one (the N-terminal region) presumably concerned with dihydrofolate and inhibitor binding and the other with dinucleotide binding. No significant sequence homology was found between larger dehydrogenases and the dihydrofolate reductases, which must, therefore, have evolved from a different ancestral protein.