Kinetic fractionation of stable carbon and nitrogen isotopes during peptide bond hydrolysis: Experimental evidence and geochemical implications

Kinetic isotope effects associated with the hydrolysis of the dipeptide glycylglycine in unbuffered aqueous solution were investigated over a 60°C temperature range. The hydrolysis of the dipeptide resulted in the distinct fractionation of carbon and nitrogen isotopes. As the extent of the hydrolysis reaction increased, the residual peptide became increasingly enriched in¹³C and¹⁵N. The kinetic isotope effect for nitrogen ranged from 1.0025 to 1.0040 and in general increased with decreasing temperature. The experimental evidence indicates that isotope effects associated with peptide bond cleavage may complicate the interpretation of stable carbon and nitrogen isotope signatures of residual proteinaceous material preserved in fossils.