CJC-1295 With DAC vs No DAC: The Chemistry of One Modification

Both forms are built on the same engineered scaffold: a 29-residue analogue of growth-hormone-releasing hormone. Native GHRH's first 29 residues — GRF(1-29) — carry full receptor activity, which made them the standard template for analogue work, but the unmodified fragment is degraded within minutes, primarily by dipeptidyl peptidase-4 clipping at the N-terminus.

The CJC-1295 backbone answers this with four amino-acid substitutions at positions 2, 8, 15, and 27, each selected against a specific liability: blocking DPP-4 cleavage, preventing asparagine rearrangement, resisting oxidation, and reducing trypsin-mediated breakdown. The result is a tetrasubstituted GRF(1-29) analogue that retains GHRH-receptor agonism while surviving far longer than the natural sequence (Jetté L, et al. Endocrinology. 2005;146(7):3052–3058).

That backbone, by itself, is CJC-1295 No DAC — approximately 3,368 Da, sometimes listed as modified GRF(1-29). Its receptor pharmacology is the GHRH receptor's: a class B GPCR signaling through Gs and raising intracellular cAMP (Mayo KE. Mol Endocrinol. 1992;6(10):1734–1744).

DAC stands for Drug Affinity Complex. Chemically, it is a maleimidopropionic-acid group attached via a short linker to a lysine residue added at the peptide's C-terminus. The maleimide is the functional part: maleimides react selectively and covalently with free thiols, and human serum albumin presents exactly one conveniently reactive free cysteine — Cys34.

So in any albumin-containing environment, the DAC-bearing peptide forms a covalent bond to albumin, converting a small, rapidly cleared peptide into a peptide-protein conjugate that persists as long as its carrier does. Albumin's circulation half-life is measured in weeks rather than minutes, and the published characterization of the DAC form reports correspondingly extended persistence relative to the unconjugated backbone (Jetté L, et al., 2005; Teichman SL, et al. J Clin Endocrinol Metab. 2006;91(3):799–805).

Two consequences worth being precise about:

• The conjugation is covalent, not adsorptive. This is a thioether bond formed by maleimide-thiol chemistry — not the reversible fatty-acid/albumin binding used by lipidated peptides such as the incretin analogues discussed in the receptor-comparison article. Both strategies exploit albumin; one ties a knot, the other holds hands.
• The receptor pharmacology is unchanged in kind. DAC alters where the molecule goes and how long it lasts, not which receptor it activates. Both forms are GHRH-receptor agonists.

In serum-free systems, the difference largely disappears. No albumin means no conjugation partner; both forms present the same receptor-binding surface, and a receptor-binding or cAMP-accumulation assay in a clean buffer measures essentially the same pharmacology. Designs that report "no difference" are frequently designs with no albumin in them.

In any albumin-containing system, the forms diverge immediately. Serum-containing media, plasma-stability assays, and whole-animal systems all supply Cys34. Once conjugated, the DAC form's effective size, distribution, and persistence change entirely — which is the whole point of the modification and the reason substituting one form for the other silently invalidates a comparison.

Blends generally specify No DAC. The co-formulated preparation covered in the CJC-1295 + Ipamorelin overview pairs the No-DAC backbone with a ghrelin-receptor agonist; the two arms of that axis are compared directly in the GHRH-class comparison.

Mass spectrometry settles which form is in the vial. The DAC modification carries a defined mass signature; the two forms are not ambiguous under identity testing. Given how frequently market listings conflate them, identity confirmation is the practical answer to a question no product label reliably answers. Certificates of Analysis are published on product pages as testing is completed — review the report before you order. Current specifications for the No-DAC form are on the CJC-1295 + Ipamorelin product page.