Analysis of PTH‐Cysteine by Adsorptive Stripping Square‐Wave Voltammetry

Abstract

The aim of this work is the study of cysteine by its derivative form. Cysteine derivation is done by Edman degradation and we obtain the phenylthiohydantoin of cysteine. Edman degradation is one of the most usual procedures for sequentate proteins. From this reaction, the phenylthiohydantoin amino acid derivative (PTH-amino acid) from the N-terminal one is obtained, leaving the new amino terminus for the next degradation cycle. To identify the produced PTH-derivative, a square-wave cathodic stripping voltammetry method is developed. In this work we show the results obtained for the optimization the instrumental and chemical conditions, and we can conclude that it is an electrochemically irreversible system with adsorptive reduction phemomenon. Under the best conditions we found a new method to analyze proteins with LOD of 2 mg L À1 and LOQ of 5 mg L À1 , a RSD less than 10% and a E r minor than 9%. Results of the application of this methodology to a real protein are included.

Establishment of a mammalian expression system for recombinant [–2]proPSA and a specific antibody against the truncated leader peptide

“…). Among them, PTH cysteine exhibited a unique property that was not detected at 269 nm, which was reported previously . Therefore, the third residue in the PSA‐ C κ fusion protein was determined to be cysteine.…”

“…Therefore, the third residue in the PSA‐ C κ fusion protein was determined to be cysteine. In Edman cycles, a carry‐over (sequence lag) effect could occur in which the signal from a previous PTH amino acid is transferred to a subsequent cycle due to incomplete coupling and cleavage of the N‐terminal residue. In this study, peaks indicating glutamic acid (E) were observed at the third and fifth residue positions of the recombinant PSA‐ C κ fusion protein; these were considered as carry‐over.…”