Abstract(L‐Cys)n+N‐base systems and (L‐Cys)n+ (L‐Lys)nsystems were studied by ir spectroscopy. It is shown that in the water‐free systems, SH ⃛N ⇌ S−⃛H+N hydrogen bonds are formed. With the (L‐Cys)n+N‐base systems, both proton‐limiting structures in the SH ⃛N ⇌ S−⃛H+N bonds have equal weight when the pKaof the protonatedN‐base is 2 pKaunits larger than that of (L‐Cys)n. The same is true with the water‐free (L‐Cys)n+ (L‐Lys)nsystem. Thus, with regard to the type of proton potentials present, these hydrogen bonds are proton‐transfer hydrogen bonds showing very large proton polarizabilities. This is confirmed by the occurrence of continua in the ir spectra. Small amounts of water open these hydrogen bonds and increase the transfer of the proton to (L‐Lys)n. In the (L‐Lys)n+N‐base systems, with increasing proton transfer the backbone of (L‐Cys)nchanges from antiparallel β‐structure to coil. In (L‐Cys)n+ (L‐Lys)n, the conformation is determined by the (L‐Lys)nconformation and changes depending on the chain length of (L‐Lys)n. Finally, the reactivity increase in the active center of fatty acid synthetase, which should be caused by the shift of a proton, is discussed on the basis of the gre