Isotopic labelling of photosystem II in Thermosynechococcus elongatus.

This report describes a protocol to incorporate isotopically labelled aromatic amino acids into the proteins of the thermophilic cyanobacterium Thermosynechoccus elongatus. By using the EPR signal of the two redox active tyrosines of Photosystem II, Tyr(D)() and Tyr(Z)(), as spectroscopic probes it is shown that labelled tyrosines can be incorporated with a high yield in this cyanobacterium. The production of a fully (13)C- or (2)H-labelled enzyme is also described.