MECHANISM FOR PROTON-TRANSFER REACTIONS OF A PEPTIDE HYDROGEN IN COPPER(2) TRIGLYCINE

The rate of interconversion of CuH-2L- and CuH-1L (where L is triglycine and the protons are ionized from the peptide linkages) is much slower than normal acid-base reactions. The rate constant for the reaction of H3O + with CuH-2L- is 4.9 × 106 M-1 sec-1, and the value for the reaction of OH- with CuH-1L is 2.5 × 104 M-1 sec-1. The reason proposed for the slower rates is the necessity to break and rearrange coordinate bonds to copper. The proton addition is general acid catalyzed and proton removal is subject to base catalysis. Two reaction paths are proposed. The copper-imide bond in CuH-2L- is not easily broken and tends to dissociate after the addition of a proton to the peptide nitrogen. © 1968, American Chemical Society. All rights reserved.