LABELING OF PROTEINS BY ISOTOPIC AMINO ACID DERIVATIVES

Abstract

The intracellular proteinase cathepsin C catalyzes a transamidation reaction between Cl4-labeled glycyl-L-tyrosinamide and insulin, leading to the labeling of the protein by substitution of an N-terminal amino acid residue. Similar transamidation reactions appear to be operative in the enzymic labeling of proteins of rat liver mitochondria upon incubation of mitochondria with Cl4-labeled tyrosinamide. The mitochondrial proteins may also be acylated by Cl4-labeled L-tyrosyladenylate or glycyl-L-tyrosyladenylate, as well as by their N-carbobenzoxy derivates; this process appears to be largely non-enzymic in nature, since it is promoted, rather than inhibited by heat denaturation of the mitochondrial proteins.