Substrate specificity of trypanothione reductase.

Trypanothione reductase, one of the family of flavin-dependent disulfide oxidoreductases, catalyses the reduction of trypanothione disulfide [N1, N8-bis(glutathionyl)spermidine] and related glutathionyl-polyamine disulfides. A series of subtly different, designed substrate analogues based on trypanothione were prepared by means of a solid-phase approach and used to study the catalytic efficiency of the parasitic enzyme. Kinetic analysis showed that the size of the polyamine bridge was relatively unimportant, for catalysis, while replacement of the ammonium bridge was much more dramatic. The highly charged glutathionylspermidine disulfide had the largest K(m) of all the substrates tested. N1-acetylcysteinylglycinyl-N8-glutathionyl spermidine and N1-glutathionyl-N8-acetylcysteinylglycinylspermidine both showed a ten-fold reduction in catalytic efficiency compared with trypanothione.