Levels of polyamines, glutathione and glutathione-spermidine conjugates during growth of the insect trypanosomatid Crithidia fasciculata

Levels of the polyamines spermidine and putrescine and the major intracellular thiols glutathione (GSH), glutathionylspermidine (GSH-SPD) and dihydrotrypanothione [bis(glutathionyl)spermidine); T[SH]₂] were measured by high performance liquid chromatography throughout the growth cycle of the insect trypanosomatid Crithidia fasciculata. The amount of total spermidine, putrescine and glutathione (free and conjugated to spermidine) was found to be elevated during growth. Of the total spermidine, 30 to 50% was found conjugated to glutathione during the exponential growth phase, increasing to 60 to 70% at stationary phase. T[SH]₂ was the principal intracellular thiol during exponential growth (12.1 to 17.4 nmol per 10⁸ cells), whereas GSH-SPD was the major thiol in stationary phase (26.2 nmol per 10⁸ cells). GSH levels changed little during the growth cycle and represented a constant proportion (10 to 12%) of the total intracellular glutathione. On dilution of stationary phase cells into fresh medium, a rapid decrease in GSH-SPD levels was observed to be associated with synthesis of T[SH]₂. This process reached 90% completion by 15 min, with steady state achieved by 120 min. As the total spermidine and glutathione pools did not increase during this interval, it could be calculated that this rapid redistribution of metabolites resulted in the release of 13 nmol per 10⁸ cells unconjugated spermidine without de novo synthesis. This mechanism for rapidly elevating the intracellular concentration of free spermidine may be advantageous to this organism in rapidly adapting to favourable growth conditions.