Transglutaminase-catalysed incorporation of putrescine into denatured cytochrome c

Abstract

Guinea pig liver transglutaminase has been used to incorporate putrescine into horse heart cytochrome $\text{c}$. The native protein showed essentially no incorporation, while ethanol-denatured cytochrome $\text{c}$ incorporated almost 1 mol putrescine per mol protein. No increase in this level of modification was obtained when maleylated cytochrome $\text{c}$ and the tryptic peptides of cytochrome $\text{c}$ were used as substrates. Analysis of the modified ethanol-denatured cytochrome $\text{c}$ by tryptic cleavage and peptide isolation showed that glutamine-42 of the intact protein is the site of incorporation of radioactively labelled putrescine. Ethanol-denatured cytochrome $\text{c}$ that was specifically modified at glutamine-42 by incorporation of putrescine could be readily renatured. The renatured modified protein showed reactivity with cytochrome $\text{c}$ oxidase comparable to that of the original native protein.