Crude peptides could comprise amounts of non-peptide impurities. The purity of custom peptide synthesis is essential and is determined by the experiment’s function. Reduction and alkylation steps didn’t affect the restoration of peptides, which don’t contain cysteine residues and due to this fact for the aim of protein identification these steps may, in principle, be omitted (23). Notably cysteine-containing peptides have been missing if reduction and alkylation steps have been skipped (Fig. 3). We subsequently concluded that at the extent of 1 pmol of protein beginning materials the strategy of protein visualization FIG. 3. Comparison of the peptide maps of the silver stained bands processed utilizing destaining, reduction, and alkylation (the higher spectrum) and using only destaining (the decrease spectrum). Blowouts reveal isotopic profiles typical for the peptide ions having arginine or lysine residues at their C-termini. We advocate together with 20% of the charged residues within the peptide sequence. Successful identification of silver stained proteins and excessive sequence coverage of MALDI peptide mass maps at the low femtomole level was reported (12), and nearly similar peptide mass fingerprints were observed in the digests of silver and Coomassie stained protein bands (13). However, different authors reported considerably lower sequence protection of peptide mass maps acquired from the digests of silver-stained proteins (8, 10, 14) that, however, could be improved by destaining of the bands prior to in-gel trypsinolysis (15, 16). We due to this fact set out to develop a method for direct and quantitative analysis of the efficiency of in-gel cleavage of proteins in order to outline a rational procedure for comparison of in-gel digestion effectivity.
Four 0.5- L aliquots of each mixed sample had been analyzed in parallel by MALDI MS as described in (13, 21) on a modified REFLEX III mass spectrometer (Bruker Daltonics, Germany). Chem. 68, 850 858. 14. Scheler, C., Lamer, S., Pan, Z., Li, X. P., Salnikow, J., and Jungblut, P. (1998) Electrophoresis 19, 918 27. 15. Gharahdaghi, F., Weinberg, C. R., Meagher, D. A., Imai, B. S., and Mische, S. M. (1999) Electrophoresis 20, 601 605. 16. Sumner, L. W., White, S., Wolf-Sumner, B., and Asirvatham, V. S. (2001) Abstracts 49th ASMS Conference on Mass Spectrometry and Allied Topics, Chicago IL. 859 860. 18. Mirgorodskaya, O. A., Kozmin, Y. P., Titov, M. I., Korner, R., Sonksen, C. P., and Roepstorff, P. (2000) Rapid Commun.
20. Fernandez-Patron, C., Calero, M., Collazo, P. R., Garcia, J. R., Madrazo, J., Musacchio, A., Soriano, F., Estrada, R., Frank, R., and Castellanos-Serra, L. R. (1995) Anal. Biochem. 224, 203 211. 21. Jensen, O. N., Podtelejnikov, A., and Mann, M. (1996) Rapid Commun. Thus we have demonstrated that application of isotopically labeled peptide standards and MALDI MS enabled direct and quantitative evaluation of the efficiency of in-gel digestion. Isotopically labeled peptides produced by digesting of a protein in H 2 18 O could possibly be employed as internal requirements for quantitative measurements by MALDI MS. A standard mixture of 18 O-labeled peptides was ready by digesting BSA with trypsin in resolution within the buffer containing H 2 18 O. Very related profiles of tryptic peptides had been detected in MALDI peptide FIG. 1. Part of the spectrum of the tryptic digest of BSA in the buffer containing H 2 18 O. Peaks in the spectrum are designated with corresponding peptide sequences and m/z calculated for the unlabeled monoisotopic ions. The aliquots containing 1 pmol of bovine serum albumin (Sigma Chemicals) in Laemmli buffer had been loaded onto separate lanes of a one-dimensional polyacrylamide gel. To arrange a regular mixture of 18 O-labeled peptides, an answer of 0.14 pmol/ L BSA in 25 mM ammonium bicarbonate buffer in H 2 18 O was digested overnight at 37 C; enzyme:substrate ratio 1:10 (w/w).
Equal volume of the mixture of 18 O-labeled peptides was spiked into the aliquots withdrawn from the experimental in-gel digests that were carried out in H 2 16 O and the samples were analyzed by MALDI MS. Relative focus of digestion products was calculated as a ratio of the depth of the monoisotopic peak of the unlabeled peptide and the intensity of the monoisotopic peak of the corresponding 2 18 O peptide customary (Fig. 2). Linearity of the calibration curve was examined by analyzing the collection of samples obtained by successive diluting of the aliquot withdrawn from the in-gel digest of 1 pmol of BSA. A 2- L aliquot was withdrawn and mixed with 1 L of an 18 O-labeled mixture of peptides (internal normal) ready as described above. The relative customary deviation of the concentrations in all collection of measurements was higher than 20%. Results and Discussion Quantification of peptides in in-gel tryptic digests. However, nobody methodology of staining provided significantly higher restoration of peptides compared to other methods within the test (Table 1). We additional tested whether the restoration of peptides from silver stained gels might be improved by destaining of protein bands prior to in-gel digestion (15). To this finish we in contrast the relative concentrations of peptides within the in-gel digests of the destained bands and of the bands treated according to the standard protocol.