<prompt> C-peptide occurs in:ProinsulinGlucagonParathormoneThyroxine  <response>: Preproinsulin contains a signal peptide of 23-amino acid. The signal peptide is removed as it enters the endoplasmic reticulum. The remainder of the molecule is pro-insulin. This peptide contains A, B chains and the connecting peptide C peptide. Separation of C peptide produces insulin. 