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Proinsulin processing in electrically permeabilized rat islets of Langerhans
D J Slee1, P M Jones, S L Howell
1Biomedical Sciences Division, King's College London.
Journal of Molecular Endocrinology
|December 1, 1990
Summary
The conversion of proinsulin to insulin in rat islets is optimal at a pH of 4.5-5.5 and requires magnesium-adenosine triphosphate (MgATP). This process is temperature-dependent and pH-sensitive, but not significantly stimulated by calcium or phorbol esters.
Area of Science:
- Endocrinology
- Cell Biology
- Biochemistry
Background:
- Insulin is a key hormone regulating glucose metabolism.
- The conversion of proinsulin to insulin occurs within secretory granules and is a critical step in insulin production.
Purpose of the Study:
- To investigate the optimal conditions for proinsulin conversion to insulin in rat islets.
- To determine the regulatory factors influencing this conversion process.
Main Methods:
- Utilized electrically permeabilized rat islets of Langerhans for controlled experimental conditions.
- Employed high-performance liquid chromatography (HPLC) for separation and analysis of radiolabeled islet proteins.
- Manipulated granular pH using ammonium acetate to assess pH-dependent conversion.
Main Results:
- Proinsulin conversion to insulin demonstrated a clear dependence on temperature and sensitivity to pH.
- Optimal conversion occurred within a pH range of 4.5-5.5, with reduced activity at pH 7.4.
- The conversion process was regulated by magnesium-adenosine triphosphate (MgATP).
- Insulin secretagogues, calcium (Ca2+) and 4β-phorbol 12-myristate 13-acetate (PMA), did not significantly stimulate conversion.
Conclusions:
- Proinsulin conversion to insulin is a complex process influenced by temperature, pH, and MgATP.
- The optimal pH for conversion is acidic, suggesting specific enzymatic requirements within the islet granules.
- Insulin secretagogues do not appear to directly regulate the conversion machinery itself.