Sermorelin

Sermorelin is the N-terminal 29-residue fragment of growth hormone releasing hormone with a C-terminal amide, and it is the shortest fragment of the native hormone reported to retain full intrinsic activity at the receptor. Unlike the CJC-1295 series it carries no engineered substitutions: it is the native sequence, which makes it the reference point against which those analogs are described.

That also means it retains every degradation liability the analogs were designed to remove. Alanine at position 2 leaves it a substrate for dipeptidyl peptidase-4. Asparagine at position 8 is prone to deamidation and succinimide rearrangement. Methionine at position 27 is prone to oxidation. Its target is the GHRH receptor, a class B G-protein-coupled receptor distinct from the ghrelin receptor engaged by the secretagogue peptides.

As the native fragment, sermorelin is the baseline in comparative stability and potency studies of the modified analogs, and much of its value in a research setting derives from that role. In-vitro work uses cAMP accumulation assays in GHRH receptor-expressing cell lines, with pituitary cell preparations for direct examination of releasing activity.

A substantial strand of reported work concerns the degradation chemistry itself: rates of dipeptidyl peptidase-4 cleavage, and the kinetics of asparagine 8 deamidation through the cyclic succinimide intermediate to a mixture of aspartyl and isoaspartyl products. That chemistry is precisely what the glutamine substitution in the modified analogs eliminates.

Reversed-phase HPLC purity and mass spectrometry identity are reported per lot on the Certificate of Analysis, with two sequence-specific attributes deserving particular attention on incoming documentation.

Deamidation at asparagine 8 adds one dalton and yields aspartyl and isoaspartyl products that are chromatographically resolvable but easily overlooked on a routine mass check; the isoaspartyl form in particular alters the backbone and is reported as substantially less active. Methionine 27 oxidation adds 16 daltons and typically resolves as a distinct earlier-eluting peak. Both can develop in correctly synthesised material that has been stored poorly, so their presence reflects handling history as much as synthesis quality.