Two synthetic peptides were completely cleaved by the cis-[Pt(en)(H2O)(2)](2+) (en is ethylenediamine) complex at pH 2.5 under thermal heating at 60 degrees C in a selective way: only the amide bonds involving the carboxylic group of the methionine residue, i.e., the Met-Z bonds (where the residue Z has a noncoordinating side chain), were hydrolyzed. Under irradiation at 300 nm, the rate constants for these cleavage reactions were approximately doubled, but side reactions occurred. Under microwave irradiation, the rate constants were increased 2-3 times at 60 degrees C and ca. 7 times at 100 degrees C, and no side reactions were detected. Microwave irradiation similarly accelerated the complete and selective cleavage of Met-Z bonds in cytochrome c at 60 degrees C in comparison with this cleavage under thermal heating, again without detected side reactions. The microwave-assisted cleavage of peptides and proteins by the platinum(II) reagent holds promise in proteomics and other biotechnological applications.