Nmr studies on complex formation of poly(L-lysine HBr) with carbonate ion in aqueous solution

✍ Scribed by Kinji Kakiuchi; Hideo Akutsu

• Publisher: Wiley (John Wiley & Sons)
• Year: 1983
• Tongue: English
• Weight: 769 KB
• Volume: 22
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360220403

✦ Synopsis

Dimer formation of poly(L-lysine HBr) in carbonate buffer a t pD 10.5 was reported in our previous paper [Biopolymers (1981) 20,345-3571. The mechanism of the dimer formation was investigated employing carbon-13 and proton nmr. pD dependence of the 13CC-nmr spectrum of poly(L-lysine HBr) in the presence of carbonate ion clearly shows that a complex formation between the COZ-ion and protonated r-amino group is involved in the stabilization of the dimer form. The lifetime of the complex is longer than s. A stoichiometric evaluation suggests that C0:-bridges two lysyl side chains. A molecular model of the dimer form designated as a single antiparallel ,&ribbon was proposed and discussed in the light of hydrodynamic and ir spectroscopic properties reported earlier. Concentration change experiments indicate that C0:binds not only to the dimer form, but also to the monomer form (a-helix). The role of the carbonate ion in the dimer formation is inferred as stabilization of the single antiparallel @-ribbon as an intermediate structure in the conversion between the a-helix and @-sheet. The a-CH proton signal of the lysine residue located in the ordered structure (a-helix and p-form) was observed to be separate from that in the random-coil region.