Studies on the binding characteristics of antimycin A and albumin in relation to the inhibitor activity of the complex on rat proximal tubular sodium transport.

As reported previously [11] Antimycin A is effective in inhibiting sodium transport of the proximal tubule only when applied to the luminal side and in the presence of albumin. Therefore the interaction of Antimycin A with albumin was examined with the technique of equilibrium dialysis. It was found that Antimycin A was bound to albumin at five sites with a dissociation constant of 2.5 X 10(-6) M. This finding suggests that Antimycin A is taken up by the tubular cell as an Antimycin A/albumin complex via pinocytosis. In the pinocytotic vesicle this complex probably dissociates, and free Antimycin A is released into the cytoplasm where it can reach it's sites of action in the mitochondria and at the plasma membrane. This uptake mechanism might provide a general method to incorporate substances into the cell which do not penetrate the plasma membrane.