Synthetic S-(2,3-dihydroxypropyl)-cysteinyl peptides derived from the N-terminus of the cytochrome subunit of the photoreaction centre of Rhodopseudomonas viridis enhance murine splenocyte proliferation

Various lipopeptides representing the N‐terminal part of the cytochrome subunit of the photosynthetic reaction centre from the purple bacterium Rhodopseudomonas virdis were prepared by solid‐phase peptide synthesis. These lipopeptides consisted of a S‐[2,3‐dihydroxypropyl]‐cysteinyl (Dhc) residue N‐terminally coupled to the nonapeptide FEPPPATTT. Different numbers of palmitoyl (Pam) chains were attached to Dhc via ester and/or amide bonds. The lipopeptide Dhc(Pam)2‐FEPPPATTT containing two ester‐bonded palmitoyl residues and a free N‐chain lipopeptide Pam‐Dhc(Pam)‐FEPPPATTT containing one amide‐ and one ester‐bonded palmitoyl residues, the two‐chain lipopeptide Pam‐Dhc(Pam)‐FEPPPATTT containing one amide‐ and one ester‐bonded palmitoyl residue, and the N‐terminally elongated lipopeptide SLVAG‐Dhc(Pam)2‐FEPPPATTT were less active. The nonapeptide FEPPPATTT and the decapeptide Dhc‐FEPPPATTT were only merginal splenocyte activators, even at concentrations as high as 1 μM. Thus, lipopeptide Dhc(Pam)2‐FEPPPATTT constitutes the first potent splenocyte stimulating Dhc‐lipopeptide described so far that contains only two fatty acid residues.