As part of the CCQM comparison strategy the BIPM in collaboration with the National Institute for Metrology of China (NIM) are coordinating the first peptide purity key comparison on, human C–peptide (diabetes differential diagnosis marker and forensic relevance) CCQM-K115/P55.2.
Primary sequence of human C-peptide: EAEDLQVGQVELGGGPGAGSLQPLALEGSLQ
The C-peptide comparison (CCQM-K115) is the first comparison addressing capabilities for the value assignment of large organic molecule primary calibrators, with C-peptide representing a model straight chain peptide with atomic weight of less than 5 kDa, in addition to being an important marker in diabetes diagnosis for which NMIs have developed CRMs and reference measurement methods. Sixteen NMIs have currently expressed interest in participation in the key comparison. The BIPM and NMI activities in peptide purity reference measurements are of interest not only to the diagnostics community, but also in the area of reference standards for peptide therapeutic products.
A model for core competency key comparisons for large molecule primary calibrators
The BIPM together with the CCQM BAWG has developed a model to classify peptides in terms of their, relative molecular mass, and the amount of cross-linking (Figure 1) as a model for the organization of comparisons on peptide purity. The degree of difficulty for the purity characterization of peptide/protein calibrators is expected to increase from quadrant A to D because of the increasing lengths of the molecules and incorporation of peptide/protein cross-links (disulfide bonds).
The CCQM-K115/P55.2 comparison for human C-peptide and other peptides of current interest identified by NMIs are marked in Figure 1. The CCQM-K115/P55.2 comparison covers the space of quadrant A for short (1 kDa to 5 kDa), non-cross-linked synthetic peptides. This comparison has been proposed after validation work was carried out by the BIPM and the NIST on angiotensin I which also fits in the space of quadrant A. Future comparisons will address the other three quadrants of the model.
|Figure 1: Model for the classification of peptides for primary structure purity comparison|