Amperometry and cyclic voltammetry of tyrosine and tryptophan‐containing oligopeptides at carbon fiber microelectrodes applied to single cell analysis

Abstract

The amperometric and cyclic voltammetric detection of a-melanocyte stimulating hormone (MSH), 0-endorphin, and corticotropin-like intermediate lobe peptide (CLIP), all proopiocortin (POC) derived peptides secreted from melanocytes of the pituitary intermediate lobe, at carbon fiber microelectrodes was investigated. For amperometry, it was found that all of these peptides could be detected; however, fouling of the electrodes reduced the response of the electrode after successive application of the peptide in flow injection experiments. The fouling wa5 apparently due to oxidation of tyrosine in the peptides as similar results were found for tyrosine but not tryptophan. The effect of fouling could be reversed if the electrode was electrochemically treated by scanning from -1 .OV to +1.OV at 300 V/s for 2 min between application of the peptides. Using cyclic voltammtery at 800 V/s, it was possible to distinguish MSH, which had a peak shaped voltammogram, from the other POC peptides, which had relatively flat voltammetric waves at this scan rate. The scan rate dependence of the peak current for MSH revealed that the voltammetry was adsorption controlled. As a result, in a monitoring application, where voltammograms are continuously obtained with a fixed interval between them, decreasing the interval increases the temporal resolution but decreases the sensitivity for MSH. It was found that when monitoring the current in the potential range of 0.90 to 1 .OOV, the temporal response to MSH was dependent upon the potential window used for scanning. Using high scan rates and a potential window of 0 to 1.2 V, it was possible to monitor exocytosis from single melanocytes and use the voltammogram to demonstrate detection of MSH from the cells.

Direct RP‐HPLC determination of underivatized amino acids with online dual UV absorbance, fluorescence, and multiple electrochemical detection

“…It was found that among the 18 solutes tested only 11 can be oxidized at carbon electrodes. The catechol-amino acids, i.e., dopa and me-dopa, as well as 5 htp, a hydroxyindole-amino acid, were the most readily oxidized solutes at l0.5 V, whereas met, i.e., S-methyl-Lhomocysteine, was oxidized only at high positive potentials A 1 V. The electroactivity of the rest of oxidizable compounds appeared at intermediate potentials between 0.5 and 1 V and it was due to the oxidation of the phenolic group for tyr, m-tyr, me-tyr, and n-tyr, the thiol group for cys and hcy, whereas for trp oxidation occurs at the indole ring [30]. The hydrodynamic voltammograms obtained are shown in Fig.…”

Quantitative determination of un-derivatised amino acids in artistic mural paintings using high-performance liquid chromatography/electrospray ionization triple quadrupole mass spectrometry

“…In addition, detection methods such as conductometry [21][22][23][24][25][26][27][28][29], electrospray ionizationtandem mass spectrometry (ESI-MS/MS) [30] or nuclear magnetic resonance spectroscopy (NMR) [31][32] can be used. Recently Petritis et al [30,33,34] reported the evaluation of an enantioselective method for the analysis of 20 un-derivatised amino acids by liquid chromatography ion spray tandem mass spectrometry using a teicoplanin-based chiral stationary phase to separate the enantiomers of the amino acids.…”

Effects of Intravesicular H+ and Extracellular H+ and Zn2+ on Insulin Secretion in Pancreatic Beta Cells

“…Recently, amperometry with microelectrodes has been applied to the study of exocytosis at a variety of cell types, including adrenal chromaffin cells (16 -19), PC12 cells (20), mast cells (21), neurons (22), and melanotrophs (23,24). Secretion is detected as a series of current spikes that correspond to detection of concentration pulses generated by exocytosis.…”