Supplementary Table 1

Name of peptide and explanation of modification Peptide sequence

Arginine – unmodified peptide GRVYATRSSAVR

Citrulline = only Citrulline amino acid residue in Position 7 GGVYAT-Cit-SSAVR

Mutated Citrulline = additional arginine in position 2 and GRVYAT-Cit-SSAVR citrulline amino acid residue in Position 7

Mutated Citrulline inverse = additional arginine in position 2 G-Cit-VYATRSSAVR is converted in citrulline (Cit) and in position 7 is an arginine amino acid residue (R)

Acetylated Ornithine = additional arginine in position 2 and GRVYAT-Orn(ac)-SSAVR acetylated ornithine amino acid residue in Position 7

Homocitrulline = additional arginine in position 2 and GRVYAT-HomoCit-SSAVR homocitrulline (HomoCit) amino acid residue in Position 7

Homocitrulline inverse = in position 2 is synthesized HomoCit G-HomoCit-VYATRSSAVR and in position 7 is an arginine amino acid residue (R)

Acetylated Lysine = additional arginine in position 2 and GRVYAT-Lys(ac)-SSAVR acetylated lysine (Lys(ac) amino acid residue in Position 7

Acetylated Lysine inverse = = in position 2 is synthesized G-Lys(ac)-VYATRSSAVR Lys(ac) and in position 7 is an arginine amino acid residue (R)

Acetylated histone GGKGGG-LysAc-AARKKA

Acetylated Non-histone SRSSGG-LysAc-GSKEAS

Supplementary Table 2

Peptide assay Cut for anti-human IgG Optical density - Mean+3*SD Arginine 0,314

Citrulline 0,273

Mutated Citrulline 0,240

Mutated Citrulline inverse 0,283

Acetylated Ornithine 0,314

Homocitrulline 0,324

Homocitrulline inverse 0,304

Acetylated Lysine 0,341

Acetylated Lysine inverse 0,331

Acetylated histone 0,287

Acetylated Non-histone 0,292

Supplementary Table 3

Peptide assay Intra-assay* CV (%) Inter-assay # CV (%)

Arginine 2.5 – 5.7 4.2 – 8.9

Citrulline 1.4 – 3.3 2.4 – 6.4

Mutated Citrulline 0.9 – 4.2 3.1 – 7.8

Mutated Citrulline inverse 2.4 – 6.1 4.2 – 9.1

Acetylated Ornithine 1.7 – 3.2 4.8 – 9.4

Homocitrulline 2.3 – 4.1 5.2 – 8.4

Homocitrulline inverse 2.2 – 4.9 6.6 – 7.3

Acetylated Lysine 1.4 – 3.8 5.1 – 9.6

Acetylated Lysine inverse 1.7 – 4.1 6.3 – 8.9

Acetylated histone 2.6 – 6.7 5.9 – 9.7

Acetylated Non-histone 2.1 – 5.9 4.2 – 8.9

* Measurements of inter-assay variability were assayed in six replicates with three samples

(low, medium and high value) in a single run.# Inter-assay precisions were determined with 4 samples in five independent tests on one day.

Supplementary Figure 1. Quality control of peptide synthesis Peptides were purified with preparative high-power liquid chromatography (HPLC) and final peptide was evaluated for purity by analytical HPLC. Chromatograms with the corresponding A280 trace are shown indicating purities of more than 88 % of each used peptide. mCit, mutated citrulline; HC, homocitrulline (carbamylation); AcOrn, acetylated ornithine; AcLys, acetylated lysine; AcHist, acetylated histone; AcNonHist, acetylated non-histone; Arg, arginine. RT, retention time.