Membranes, material transfer and enzymes

Abstract

A linear three-compartment material transfer system was constructed. The terminal phases, α and β, of the model system were separated from a central compartment by cellophane membranes, and phase α was perfused at a constant rate with an aqueous solution of urea, maleic acid, lithium and potassium chlorides. Addition of urease to the central compartment initiated a spontaneous chemical reaction, the enzymatic hydrolysis of urea, and thereby provided the system with an Internal source of chemical energy. Thereafter, the system slowly evolved toward a nonequilibrium stationary state. The actual stationary state reached depended upon the perfusion rate, the composition of the perfusion fluid, the permeability of the membranes to the chemical species present in the system, and the activity of the enzyme preparation. If the composition of all phases at the time of the addition of urease were the same as that of the perfusion fluid, distributant ions moved through the membrane against their concentration gradients during the approach toward a stationary state. Distributant ions were selectively concentrated in one or the other of the terminal phases. It was found that the logarithm of the distributant ion selectivity ratio was a near linear function of the ammonia production rate of the system. A physical chemical analysis of the behavior of the system is attempted, and practical equations useful in the description of the behavior of such systems are derived.