Anglerfish make two forms of somatostatin-28 from the same gene — one with a rare modified amino acid — showing nature can fine-tune peptides after they are made.
16-dalton differenceBetween hydroxylated and non-hydroxylated forms of the same peptide
What the researchers found
Two versions of somatostatin-28 were isolated from anglerfish tissue. Both came from the same gene, but one had a modified amino acid: 5-hydroxylysine at position 23.
Mass spectrometry confirmed the two forms had molecular weights of 3,220 (hydroxylated) and 3,204 (non-hydroxylated). The 16-unit difference matches exactly what adding one oxygen atom would do.
This was the first documented case of a hydroxylated peptide hormone. Before this, hydroxylysine was known almost exclusively from collagen (the protein that gives skin and bones their structure).
Why it matters
This changed what scientists thought about peptide hormone modifications. Finding hydroxylysine in a hormone meant that post-translational modifications (chemical changes made after a protein is built) are more widespread than previously believed. It opened questions about whether similar modifications exist in human peptide hormones.
How the study worked
Researchers isolated peptide fractions from anglerfish pancreatic islets. They identified the two somatostatin-28 forms using amino acid sequence analysis, gas chromatography/mass spectrometry for the hydroxylysine, and fast-atom bombardment mass spectrometry for molecular weight confirmation. Proteolytic fragment analysis pinpointed the modification to position 23.
What this study cannot tell us
This study examined only anglerfish somatostatin. It did not determine whether the hydroxylation affects the peptide's biological activity. It is unknown whether mammalian somatostatins carry the same modification.
How to read the evidence
Preliminary in-vitro biochemistry study from a single species with no functional testing of the modification.
When this study was published
Published in 1984 — early discovery of post-translational modification in peptide hormones.
The bigger picture
Post-translational modifications like hydroxylation expand the functional diversity of peptides beyond what genes alone encode. This principle is now central to understanding how cells create specialized signaling molecules.
Questions still open
- Does hydroxylation change somatostatin-28 biological activity?
- Is this modification found in mammalian somatostatin peptides?
Common questions
What is somatostatin?
What is hydroxylysine?
Read the original research
Anglerfish preprosomatostatin II is processed to somatostatin-28 and contains hydroxylysine at residue 23.
The Journal of biological chemistry, 259(24), 15021-4
Citation
Andrews, P C; Hawke, D; Shively, J E; Dixon, J E. (1984). Anglerfish preprosomatostatin II is processed to somatostatin-28 and contains hydroxylysine at residue 23.. The Journal of biological chemistry, 259(24), 15021-4.