C-peptide seen in?

C-peptide seen in?
a) In Pre-proinsulin
b) In Proinsulin
c) As a combined entity with insulin after secretion
d) A gastrointestinal proactive molecul
Correct Answer - B
Ans: B. In proinsulin
Synthesis of insulin:
Synthesized as larger preprohormone (Pre-proinsulin) entering ER.
Removal of 23 amino-acid signal peptide takes place.
Converted to “Prohormone -Proinsulin”.
Proinsulin structure:
Made up A & B chain, connected by C-peptide/chain.
C-peptide –
Detached from granules before secretion.
90% – 97% insulin from B cells.
Along with equimolar amounts of C-peptide.