Peptide maps at picomolar levels obtained by reversed-phase high-performance liquid chromatography and pre-column derivatization with phenyl isothiocyanate. Microsequencing of Phenylthiocarbamyl Peptides

Femtomole peptide mapping by derivatization, high-performance liquid chromatography, and fluorescence detection

A highly sensitive peptide mapping method using derivatization and fluorescence detection is described. Bovine cytochrome c was digested using a buffer compatible with the derivatization that followed. The derivatization was performed with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate. The peptide mapping of the tagged digest was conducted with both HPLC and capillary LC (CLC) systems. A capillary LC-electrospray ionization mass spectrometer (MS) was set up for measuring the molecular weights of the tagged peptides. Optimization was made of the conditions used for digestion, derivatization, and mapping. MS measurements of the tagged peptides suggested that there was only one derivatization product produced from all peptides (except one) and that all the identified peptides were fully tagged. Peptide mapping of the tagged digest reviews a larger number of peptides, covering almost the entire sequence. Peptide mapping of a 20 fmol amount of tagged digest was readily performed with the CLC system. By using derivatization and fluorescence detection, the sensitivity of peptide mapping could be improved 2000 times compared to that observed with uv detection of untagged peptides.

Semi-automated chromatographic procedure for the isolation of acetylated N-terminal fragments from protein digests

Several published procedures have been combined to develop a general strategy for the specific identification and isolation of the acetylated-N-terminal fragment from all other proteolytic fragments. This ruse can be divided into four steps: (i) succinylation of the substrate to block lysine NH2 groups; (ii) enzymatic digestion of the modified protein; (iii) automated phenylisothiocyanate derivatization of the protease derived fragments to block newly generated "free" N-termini; and (iv) reversed-phase high-performance liquid chromatography with on-line photodiode array spectroscopy. The individual phenylthiocarbamyl-peptide species exhibit an increased reversed-phase retention time and a greater UV (210-297 nm) profile compared to the corresponding control (-phenylisothiocyanate) digest. The N-terminal acetylated fragment shows neither a retention time shift nor an augmented UV profile. To validate each process step, synthetic peptides and acetylated-N-terminal proteins of known sequence were used as test samples. The desired fragment was isolated from three proteins and positively identified by electrospray mass spectrometry and amino acid composition. Proteins with other N-terminal blocking groups should be amenable to this procedure.