On the use of polyethylenimine as a carrier for protein sequencing: comparison with polybrene

In the gas-liquid phase automated protein sequencer, polyethylenimine was used as a hydrophilic entrapping polymer. Glass fiber filters soaked in 0.3% solution of polyethylenimine were used. Sperm whale myoglobin, beta-lactoglobulin, and several peptides with basic or acidic pI were sequenced. Loads from 20 to 26,000 pmol were tested. Initial and repetitive yields compare favorably to those obtained with polybrene-coated glass fiber filters. Recovery of individual amino acids shows that none gave a particularly low yield, in contrast with the low recovery of Arg, Trp, His, Glu, and Asp when polybrene was used. The usual artefacts were greatly diminished and even disappeared as in the case of N,N'-diphenylurea. Substitution of polyethylenimine for polybrene sped up the analysis because the precycling employed to condition polybrene-coated glass fiber filters was no longer necessary. In conclusion polyethylenimine appears superior to polybrene for sequencing protein and peptides.