conservation of C-peptide sequence in the guinea pig
The NCBI Nucleotide database can be used to search for coding sequences (mRNA and translated protein) of genes. You need to enter the name of the gene (INS) or protein (insulin) and then species (use either the common name, "guinea pig" or the scientific name, "Cavla porcellus").

Filter the results to show you only mRNA coding sequences (sometimes abbreviated as "complete CDS"). These entries are annotated with the regions that account for the signal peptide, mature peptide(s) and prodomain(s). In your case, the full proinsulin is annotated as mature peptide and the B and A chains. The C peptide connects the A and B chains, located between the only two dibasic sites (R55R56 and K88R89).

Another useful database is the UniProt Protein Knowledge Base which presents similar information in a slightly more graphical presentation. Here is guinea pig insulin in this database.

If you happen to compile a whole list of C-peptide domains from other mammals, then you can use an alignment tool like ClustalOmega to align the peptide sequences to look for commonalities.

As for guinea pigs, there is only a single insulin gene (like most mammals). Only mice and rats have a two gene insulin system, Ins1 and Ins2. Generally speaking, there is poor conservation of the C peptide domain across mammals, in part because it only serves to link the A and B chains together to form the necessary disulfide bridges.

If you are wondering whether an anti-guinea pig antibody will cross react with another species' epitope, that information is listed on the antibody specification sheet under species cross-reactivity. Some antibodies are more cross-reactive than others, and you will need to refer to the specific manufacturer's information to be sure. 


Wang S, Wei W, Zheng Y, Hou J, Dou Y, et al. (2012) The Role of Insulin C-Peptide in the Coevolution Analyses of the Insulin Signaling Pathway: A Hint for Its Functions. PLoS ONE 7(12): e52847. doi:10.1371/journal.pone.0052847 A note on this paper, I would not take the conclusions that C-peptide has a physiological role in intracellular or endocrine signalling because it is still quite a controversial issue. I used this article because it was open access and to demonstrate in Figure 1 the variability of the C-peptide domain across selected mammals.