Distribution of urocanic acid isomers between aqueous solutions and n-octanol, liposomes or bovine serum albumin.
The distribution of urocanic acid (UCA) isomers between aqueous solutions and n-octanol, egg yolk phosphatidylcholine (eggPC) liposomes or bovine serum albumin (BSA) has been evaluated. Regarding its partitioning between water and n-octanol, the behaviour of both isomers is very similar, and the amount incorporated to the organic solvent is mostly determined by the fraction of the compound that, in the aqueous phase, is present as uncharged species. This implies that the highest hydrophobicity occurs near the isoelectric point. cis- and trans-UCA are readily incorporated into eggPC unilamellar liposomes. A simple pseudophase treatment of ultrafiltration data renders a binding constant of 0.20+/-0.04mL/mg for the trans isomer at pH 7.4. The binding constant decreases, by a factor two, at pH 5.0, suggesting that the negatively charged species is more favourably bound to the liposomes than the neutral species, which is mostly present as zwitterions. The cis-isomer, at both pHs, is less incorporated to the bilayers. trans-UCA and cis-UCA readily bind to BSA at pH 7.4, with binding constants of 3400M(-1) and 6900M(-1), respectively. This result suggests that, as in the octanol/water partitioning, hydrophobic interactions predominate and the degree of binding is determined by the fraction present as uncharged species. A smaller binding constant at pH 5.0 indicates that the charge of the protein is also plying a relevant role.
Departamento de Química, Facultad de Química y Biología, Universidad de Santiago de Chile, USACH, Av. B O'Higgins 3363, Chile.
Ana M
AM
Campos
Carlos
C
Cárcamo
Eduardo
E
Silva
Sandra
S
García
Else
E
Lemp
Emilio
E
Alarcón
Ana María
AM
Edwards
German
G
Günther
Eduardo
E
Lissi
D020003:1-Octanol / Q000737:chemistry*; D000818:Animals; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D008081:Liposomes / Q000737:chemistry; D015394:Molecular Structure; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D012996:Solutions; D014560:Urocanic Acid / Q000737:chemistry*; D014867:Water / Q000737:chemistry
D008081:Liposomes; D012996:Solutions; D014867:Water; D012710:Serum Albumin, Bovine; D014560:Urocanic Acid; D020003:1-Octanol