Proinsulin precursors in catfish pancreatic islets

Area of Science:

• Endocrinology
• Molecular Biology
• Biochemistry

Background:

• Insulin biosynthesis involves the processing of precursor proteins.
• The precise molecular mechanisms of insulin precursor processing in fish are not fully elucidated.

Purpose of the Study:

• To investigate the existence and characteristics of insulin-related peptides larger than proinsulin in catfish pancreatic islet cells.
• To determine the relationship between these larger peptides and proinsulin/insulin synthesis.

Main Methods:

• Incubation of catfish pancreatic islets with radiolabeled amino acids.
• Analysis of synthesized peptides using SDS-PAGE, electrophoresis, tryptic peptide analysis, and immunoprecipitation with anti-insulin antibody.
• Investigation of precursor-product relationships using pulse-chase experiments and cycloheximide treatment.

Main Results:

• Two acid-alcohol-extractable peptides (12K and 11K) larger than proinsulin were detected.
• The 12K protein exhibited characteristics of catfish preproinsulin.
• Both 12K and 11K proteins were chemically related to insulin and proinsulin, bound to anti-insulin antibody, and showed a precursor-product relationship with proinsulin and insulin.

Conclusions:

• Catfish pancreatic islet cells synthesize insulin-related peptides (preproinsulin and an 11K protein) that are precursors to proinsulin.
• The conversion of these precursors to proinsulin is a post-translational event in fish.