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Kinetics of proinsulin conversion in human islets
S Sizonenko1, J C Irminger, L Buhler
1Laboratoires de Recherche Louis Jeantet, Centre Médical Universitaire, Geneva, Switzerland.
Diabetes
|June 1, 1993
Summary
Human proinsulin conversion in pancreatic islets shows intermediates accumulate, with des 31.32 split proinsulin accumulating more than des 64.65 split proinsulin due to slower C-peptide conversion.
Area of Science:
- Biochemistry
- Endocrinology
- Cell Biology
Background:
- Proinsulin is the precursor to insulin, undergoing complex post-translational modifications.
- Understanding proinsulin conversion is crucial for insights into insulin production and potential diabetes-related mechanisms.
Purpose of the Study:
- To investigate the kinetics of proinsulin conversion intermediates in human pancreatic islets.
- To identify specific cleavage sites and their relative conversion rates during insulin biosynthesis.
Main Methods:
- Human pancreatic islets were pulse-labeled with [3H]leucine.
- Isotopically labeled proinsulin and its conversion products were analyzed using reversed-phase HPLC.
- Time-course analysis was performed over a 180-minute chase period.
Main Results:
- Fully processed insulin appeared with a half-time of 100 minutes, delayed by intermediate accumulation.
- Des 64.65 split proinsulin was a minor intermediate (max 5.2%).
- Des 31.32 split proinsulin accumulated significantly (max 29.3%), indicating slower cleavage at the C-peptide/A-chain junction.
Conclusions:
- The conversion of human proinsulin is characterized by the accumulation of specific intermediates.
- Slower conversion at the C-peptide/A-chain junction compared to the B-chain/C-peptide junction dictates the accumulation pattern.
- The findings explain the presence of des 31.32 split proinsulin in circulation.