• Lilly Research Laboratories, Eli Lilly & Company, Indianapolis, IN46285, USA

Human K2 EDTA and P800 plasma (500 μl) was spiked with proglucagon 33–61, 35–61 and 36–61 stable-isotope-labeled internal standard peptides (CPC Scientific, custom order) and diluted with I buffer (25 mmol/l Tris-HCl, 25 mmol/l HEPES, 300 mmol/l NaCl, 0.1% (v/v) octyl β-D-glucopyranoside, pH 7.5).

• Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA

Homologous and heterologous competition experiments were performed with non-radioactive peptide analogues[127I]-Tyr1-GIP(1-42) and [127]-Tyr10-GIP(1-42) to ensure quantification of the high-affinity binding site of the GIPR. Peptide analogues were generated using synthetic [127I]-Tyr amino acid building blocks (CPC Scientific).

1. Janssen Research and Development, 3210 Merryfield Row, San Diego, CA 92121, USA.
2. Foundation for the National Institutes of Health, North Bethesda, Maryland, USA
3. Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
4. Merck & Co., Inc., West Point, Pennsylvania, USA

Purified synthetic stable isotope (15N and 13C) labeled (SIL) peptides were from CPC Scientific (EDSLEAGLPLQVR [CMGA]; SLGVGFATR [FABPH]; VLEYLNQEK [SCG2]; and THLGEALAPLSK [VGF]); and JPT Peptide Technologies (TNYLYGK [NPTX2]).

• Departments of Infectious Diseases, OMNI Bioinformatics, Chemistry, Structural Biology, Biochemical and Cellular Pharmacology, Translational Immunology, Pathology, Molecular Biology, Genentech, South San Francisco, California, USA

MQLNKV-L(U13C6,15N)-KGL(U13C6,15N)MIALPVMAIAA-dipalmitoyl2C-SSNKNGG-K-biotin, which upon cleavage by LspA, yields the product peptide dipalmitoyl2C-SSNKNGG-K-biotin. A product standard [dipalmitoyl2C-SSNKNAAK-(NHCH2CH2NH)-biotin; CPC Scientific] was in the reaction mixture as an internal standard for normalization of product quantitation.

Synthetic Hcrt1 with13Cand15N stabile isotopemodification on two leucine amino acids was used for internalstandard (ISTD) calibration; Glp-P-L(U13C6,15N)PDCCR-QKTCSCR-L(U13C6,15N)YELLHGAGNHAAGILTL-NH2(CPC Scientific, Sunnyvale, CA)

"The internal standard (ISTD) WIL*GDVFIREYYSV*FDR was ordered from CPC Scientific (Sunnyvale, Calif., USA) and contained L*6×13C 1×15N and V*5×13C 1×15N. The ISTD contained an internal trypsin cleavage site in order to monitor the digestion with trypsin to completion."

• 1 Lilly Research Laboratories, Eli Lilly & Company, Lilly Corporate Center, Indianapolis, IN 46285, USA.

"The OXM peptides 1–37, 3–37 and 4–37 as well as their corresponding stable isotope-labeled internal standards (each containing one [ 13 C 9 , 15 N]-labeled phenylalanine and two [ 13 C 6 , 15 N]-labeled leucine residues) were synthesized by CPC Scientific, Inc."

• Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, IN 46285, U.S.A

"Stable isotope-labelled (SIL) peptides were synthesized by CPC Scientific. Leucine residues were selectively labeled using 13C/15N-labelled amino acids resulting in the addition of 7 Da to the peptide mass (Supplementary Table S1). The reported purity of each synthesized peptide was more than 95% based on HPLC analysis. "

• Cardio-metabolic Disease Biomarkers, Merck Research Laboratories, Kenilworth, NJ., Merck & Co., Inc.

"Glucagon synthetic peptide and heavy isotope–labeled internal standards (ISs) of oxyntomodulin and glucagon containing 2 [ 13 C 6 - 15 N]-labeled leucines and 1 [ 13 C 9 - 15 N]-labeled phenylalanine were synthesized by CPC Scientific.."

• Screening and Protein Sciences, Merck Research Labs, North Wales, PA, USA

Plates were incubated for 210 min at 25 °C followed by quenching with 25 uL water with 2% formic acid containing 600 nM of the internal standard with the sequence KTEEISEVN[L-U7]-OH (CPC Scientific).