Fat metabolism in higher plants

The permeability of chloroplast membranes to acetate was studied by measuring the direct movement of radioactive acetate into the organelle. The half-time for equilibration of 1 m m acetate across the envelope membrane was less than 5 sec while that for the lamellar membranes was greater than 30 min at pH 7.9. Evidence suggested that the undissociated acid penetrated faster than the acetate anion. Acetate was bound by the chloroplasts with an optimum pH of 6.5. The binding was enhanced fourfold by Mn2+ and Mg2+ with a reversal of the enhancement by EDTA. Binding was weak and saturated at 15–30 nmoles acetate/mg chlorophyll. It appeared that acetate was bound in the vicinity of the lamellar membranes. Permeation of acetate was much faster than and without effect on that of glutamate.