The major advantage of carbohydrate counting is that it adds yet another level of flexibility to the general issue of diet/calories and the relationship to insulin, perhaps the most important, least emphasized and least understood aspect of diabetes therapy. Historically, patients have made guesses (sometimes educated ones) about how much additional insulin to administer for added food. To a great extent, carbohydrate counting minimizes such estimations. Clearly, however, support and education from an experienced nutritionist are required for optimal results.
Proinsulin undergoes maturation into active insulin through the action of cellular endopeptidases known as prohormone convertases ( PC1 and PC2 ), as well as the exoprotease carboxypeptidase E .  The endopeptidases cleave at 2 positions, releasing a fragment called the C-peptide , and leaving 2 peptide chains, the B- and A- chains, linked by 2 disulfide bonds. The cleavage sites are each located after a pair of basic residues (lysine-64 and arginine-65, and arginine-31 and −32). After cleavage of the C-peptide, these 2 pairs of basic residues are removed by the carboxypeptidase.  The C-peptide is the central portion of proinsulin, and the primary sequence of proinsulin goes in the order "B-C-A" (the B and A chains were identified on the basis of mass and the C-peptide was discovered later).