muramidase and phenylisothiocyanate

Cysteine residues in polypeptides are not easily identified during automated N-terminal sequence analysis. Reaction of cysteine side chains with 4-vinylpyridine and identification as the pyridylethylated phenylthiohydantion derivative (PE-PTH-Cys) were proposed. However, after this reaction a desalting step is necessary. If limited sample amounts do not allow this desalting step, on-sequencer pyridylethylation is an alternative, although preview of the consecutive amino acid is usually observed in this case. We describe an on-sequencer procedure that avoids such preview formation by derivatizing the peptide with phenylisothiocyanate (PITC) prior to reaction with 4-vinylpyridine. The pyridylethylation is performed in the cartridge of the sequencer after immobilization of the protein or peptide on a polybrene-coated glass fiber filter and thiocarbamylation with PITC. Preview caused by N-alkylation is not observed and PE-PTH-Cys is detected in much higher yields than usual. The procedure reported here is significantly shortened, optimized to reduce side products, and avoids losses during sample handling. It can easily be adapted to any automated version of the sequencers.

Topics: Amino Acid Sequence; Bacterial Proteins; Cysteine; Isothiocyanates; Methods; Molecular Sequence Data; Muramidase; Pyridines; Ribosomal Proteins; Thiocyanates

A method for analysis of phenylthiocarbamyl-amino acids by HPLC is described. Solvent A contains 0.05 M sodium acetate plus triethylamine (2.75 ml/liter) adjusted to pH 6.40 with phosphoric acid. Solvent B consists of 50% solvent A, 40% acetonitrile, and 10% methanol. The stationary phase is a 3-micron Spherisorb ODS-2 column (4.6 X 100 mm). A new sample can be injected every 27 min. Variation of the triethylamine concentration from 1 to 4 ml/liter is shown to affect column selectivity in a predictable manner, and this provides a rational basis for optimizing chromatographic conditions. Resolution of certain hydrophilic amino acids (Arg, Thr, Ala, and Pro), and mobile phase stability are improved over previously described procedures.

Topics: Amino Acids; Autoanalysis; Chromatography, High Pressure Liquid; Egg White; Ethylamines; Fibrinopeptide A; Isothiocyanates; Muramidase; Thiocyanates

Methods for the quantitative derivatization of amino acids with phenylisothiocyanate and for the separation and quantitation of the resulting phenylthiocarbamyl derivatives by reverse-phase high-performance liquid chromatography are described. Phenylthiocarbamylation of amino acids proceeds smoothly in 5 to 10 min at room temperature. Coupling solvents, reagent, and some byproducts are removed by rotary evaporation under high vacuum, and the phenylthiocarbamyl derivatives are dissolved in 0.05 M ammonium acetate, pH 6.8, for injection onto the octyl or octadecylsilyl reverse-phase column. Columns are equilibrated with the same solvent and the effluent stream is monitored continuously at 254 nm for detection of the amino acid derivatives. Elution of all of the phenylthiocarbamyl amino acids is achieved in about 30 min utilizing gradients of increasing concentrations of ammonium acetate and acetonitrile or methanol. This approach to amino acid analysis offers select advantages, both with respect to methods which employ reverse-phase separation of prederivatized samples and to the classical ion-exchange procedure. All amino acids, including proline, are converted quantitatively to phenylthiocarbamyl compounds and these are stable enough to eliminate any need for in-line derivatization. Furthermore, results comparable in sensitivity and precision to those obtained by state-of-the-art ion-exchange analyzers may be generated with equipment that need not be dedicated to a single application.

Topics: Amino Acids; Animals; Cattle; Chromatography, High Pressure Liquid; Isothiocyanates; Muramidase; Peptides; Ribonuclease, Pancreatic; Thiocyanates