We have studied the conductivity properties of two reversing sequenceamphiphilic synthetic peptides which have a lipid-like behavior at air/waterinterface with an enriched tyrosine domain that undergoes di-Tyr formation uponsurface illumination.
We have measure lateral conductivity in the monomolecular layer in absent orpresence of a negative plaque of polarization beneath of the peptide array. Wehave also designed a second circuit able to measure the semiconductor-diodebehavior of the confined peptide in a close packed two dimensional array. Both peptides are retro isomers with the same amphiphilicity but differing inthe asymmetry of peptide bond direction named as PF3 Ac-KKGALLLLLGYYY-NH2 andPF4 peptide Ac-YYYGLLLLLAGKK-NH2. Both peptide monolayers undergodi-Tyr formation when they are illuminated directly to the surface detected byboth fluorescence and RAMAN spectroscopy. The di-Tyr formation induces surfaceheterogeneity detected by BAM microscopy.
Both peptides are able to laterally conduct electrons almost 8 times higherthan DMPC phospholipid. The PF4 conductivity was higher than PF3 and can beattributed to the C®N orientation of PF4. Therefore, we observed an asymmetryin conductivity due to peptide bond orientation even when the surfaceproperties of both peptides are almost identical. The di-Tyr formationincreases the conductivity properties of both peptides, suggesting that thelaterally formation of Tyr cross-linking enhance lateral conductance.
When we measure the current against voltage for each peptide underappropriate condition evaluating that both have semiconductor-diode properties.The electron flow is facilitated from the C-terminus to the N-terminuscoinciding with the ?N?(C=O)? peptide bond orientation when compared withthe reversal flow from N-terminus to C-terminus. Assimilating the peptidebackbone as a diode system connected in series where the N materialpart is represented by the oxygen whereas nitrogenwould correspond to the P material part of the semiconductor.We propose that this conductivity asymmetry may be of biological importance inpolytopic transmembrane proteins.
