Rat proinsulin I is converted into insulin more rapidly than is proinsulin II. To study this further, rat islets were labelled (10 min) and conversion kinetics of the labelled proinsulins were monitored during a 120 min chase. Proinsulins, conversion intermediates and both insulins were separated by h.p.l.c. The accumulation of des-64,65-(split proinsulin II) during the chase suggests that the B-chain/C-peptide junction of proinsulin II is cleaved more slowly than the equivalent site on proinsulin I. This accounts for the differential kinetics of conversion of proinsulins I and II, and is presumed to be caused by one (or more) of the amino acid replacements which distinguish the two proinsulins.
Differential rates of conversion of rat proinsulins I and II. Evidence for slow cleavage at the B-chain/C-peptide junction of proinsulin II
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S V Sizonenko, P A Halban; Differential rates of conversion of rat proinsulins I and II. Evidence for slow cleavage at the B-chain/C-peptide junction of proinsulin II. Biochem J 15 September 1991; 278 (3): 621–625. doi: https://doi.org/10.1042/bj2780621
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