Noun
English Wikipedia has an article on:proinsulinWikipedia
proinsulin (countable and uncountable, plural proinsulins)
(biochemistry) A polypeptide that is the prohormone precursor of insulin
About 5–10 min after its assembly in the endoplasmic reticulum, proinsulin is transported to the trans-Golgi network (TGN) where immature granules are formed. Source: Internet
The C-peptide of proinsulin (discussed later), however, differs much more among species; it is also a hormone, but a secondary one. Source: Internet