Human serum albumin as a catalyst of RNA cleavage: N-Homocysteinylation and N-phosphorylation by oligonucleotide affinity reagent alter the reactivity of the protein

Kinetic parameters for the cleavage of UpA site in an oligonucleotide in the presence of human serum albumin (HSA) or one of its clinically relevant modification were measured. The RNA-hydrolyzing activity of HSA was decreased by its nonenzymatic N-homocysteinylation. According to 31P NMR data, Lys and Tyr residues were the labeling targets when a phosphorylating analog of oligoribonucleotide substrate was employed. The site of tyrosine modification was slowly dephosphorylated. Lys-directed affinity labeling suppressed oligonucleotide cleavage indicating that lysines took part in the reaction.