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Structural properties of the creatine-kinase active site studied by chromophoric-reagent labelling.

The environment of the active site of creatine kinase has been investigated by means of three chromophoric reagents: 2-hydroxy-5-nitrobenzyl bromide, 2-methoxy-5-nitrobenzyl bromide and 2-(dansylamino)ethyl monophosphate. 
 
 
 
1 
The first two reagents are incorporated at the essential thiol groups. The effect of pH on the spectra of the 2-hydroxy-5-nitrobenzyl-labelled creatine kinase suggests that this reagent lies inside the active site near an ionized residue, while the 2-methoxy-5-nitrobenzyl group is apparently exposed to the medium. Conformational changes induced by the binding of different ligands, including nucleotide substrates or anions, produce only perturbations of the 2-hydroxy-5-nitro-benzyl chromophore. 
 
2 
The 2-(dansylamino)ethyl monophosphate (which is really an analogue of the nucleotide substrate) interacts with the nucleotide site of creatine and arginine kinases in a relatively hydrophobic environment.