Catalytic actions of synthetic polypeptides: 2. stereoselective inhibition of ascorbic acid oxidation by the basic polypeptide-copper (II) complexes

Abstract

The oxidation of l-ascorbic acid and d-isoascorbic acid by the poly( l-lysine) (PLL), poly( d-lysine) (PDL), poly( l-ornithine), poly( l-arginine) and poly( l-histidne) Cu(II) complexes in phosphate buffer has been investigated. Most polypeptide-Cu(II) complexes showed an inhibitory effect. However, a comparison of the initial velocities of the enantiomeric polypeptide Cu(II) complexes gave the stereoselectivity indices ( V O) PDL cu/( V O) PLL-Cu = 2.8 on l-ascorbic acid and 1.8 on d-isoascorbic acid at pH 5. At alkaline pH, the reverse was found for the stereoselective oxidation. At pH 10.5, the indices were calculated to be 0.7 on both ascorbic acids.