Analysis of dipeptides by reversed-phase high-performance liquid chromatography without derivatization using amperometric detection on a copper electrode

Direct determination of amino acids by capillary electrophoresis/electrochemistry using a copper microelectrode and zwitterionic buffers

Sixteen free amino acids were separated by capillary electrophoresis (CE) using zwitterionic buffers of pH 9.8 and detected amperometrically using a copper microelectrode. Low conductivity buffers make possible the use of higher buffer concentrations. This depresses the electroosmotic flow, leading to a better separation of the amino acids compared to that obtained using strong electrolytes. The use of zwitterionic buffers also minimizes the amount of Joule heating in the capillary leading to more efficient separations. Perhaps most importantly for electrochemical (EC) detection, these buffers reduce the noise due to high separation current at the EC detector. The increased signal-to-noise ratio (S/N) results in much better detection limits for amino acids than those reported previously for capillary electrophoresis/electrochemistry (CEEC) with a copper electrode. Detection limits ranged from 10 to 400 nM, and the response was linear over three orders of magnitude for most of the amino acids. The system demonstrated good long-term stability and reproducibility with a relative standard deviation (RSD) of less than 5% for both the migration time and peak current (n = 20). This method was employed for the determination of amino acids in urine and in brain microdialysate samples.

Determination of peptides by capillary electrophoresis-electrochemical detection using on-column Cu(II) complexation

A Cu(II)-coated capillary has been developed for the determination of peptides by capillary electrophoresis with electrochemical detection. Capillaries were prepared by forcing a solution 48 microM in CuSO4, 120 microM in tartaric acid, 2.4 mM in NaOH and 120 microM in KI through them for 25 min; the resulting capillaries are stable for at least 12 h. Under alkaline conditions, peptides complex with Cu(II) present on the walls of the capillary to form Cu(II)-peptide complexes which can be detected oxidatively at a carbon fiber electrode. Di-, tri-, tetra- and pentaglycine were determined with a detection limit of 7 x 10(-7) M for triglycine. N-Terminal-blocked peptides can also be determined via this method. This system is more sensitive than direct detection of peptides by UV at 210 nm and exhibits higher selectivity than commonly employed derivatization procedures based on reactions with a primary amine functionality.

Purification and partial characterization of a transcription-inhibitory peptide from Tetrahymena

The protozoa Tetrahymena excretes a small peptide complex with an Mr of about 5,000. The peptide inhibits transcription by reducing the activity of the RNA polymerase. We have purified and partially characterized the peptide complex. It contains two peptide chains of apparent Mr 2,300 and 2,600, respectively. Magnesium ions in connection with the SH groups of cysteine play a role in holding together the two chains of the intact complex.