Glutathionylspermidine metabolism in Escherichia coli

Intracellular levels of glutathione and glutathionylspermidine conjugates have been measured throughout the growth phases of Escherichia coli. Glutathionylspermidine was present in mid-log-phase cells, and under stationary and anaerobic growth conditions accounted for 80% of the total glutathione content. N¹,N⁸-bis(glutathionyl)spermidine (trypanothione) was undetectable under all growth conditions. The catalytic constant k(cat.)/K(m)) of recombinant E. coli glutathione reductase for glutathionylspermidine disulphide was approx. 11000-fold lower than that for glutathione disulphide. The much higher catalytic constant for the mixed disulphide of glutathione and glutathionylspermidine (11% that of GSSG), suggests a possible explanation for the low turnover of trypanothione disulphide by E. coli glutathione reductase, given the apparent lack of a specific glutathionylspermidine disulphide reductase in E. coli.