activating agents, we used the carbodiimide 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide (EDC) and prebiotically plausible condensing agents 2cyanoguanidine, cyanamide, dicyanamide, and methyl isocyanide (MIC). We used the activating agents to form the transient acyl phosphates of the acid and alkyl phosphates-a double-tailed amphiphile with an anionic phosphate head group (Figure ). All of these components of the reaction cycle were well soluble in the 100 mM range in pyridinecontaining MES-buffered water (200 mM), provided the pH remains above pH 6. Pyridine was added because of its ability to suppress the formation of N-acyl urea and to aid acyl phosphate formation. We performed all experiments at 37 °C and under constant stirring.