Selective disulphide linkage of plant thionins with other proteins.

Thionins are shown to form disulphide linkages with other proteins. The reaction with bacterial enzymes beta-glucuronidase and neomycin phosphotransferase II could be prevented and reversed with dithiothreitol and blocked with N-ethylmaleimide. Other cysteine-rich low-molecular-weight toxic peptides from plants (LTP-3 from barley and P19 from potato) did not react as the thionins. Certain cysteine-containing proteins, such bovine serum albumin, ovalbumin and cytochrome c, reacted with thionins, while others, including carbonic anhydrase, soybean trypsin inhibitor, bovine-lung trypsin inhibitor and phosphorylase B did not. Selectivity of the reaction with a periplasmic component of the phytopathogenic bacterium Pseudomonas solanacearum was also shown.