EVIDENCE FOR DIVALENT METAL SEQUESTRATION BY DOG KIDNEY MICROSOMES.

Abstract : The binding of Mn(2+) ion to ATP was determined utilizing the characteristic six-line electron spin resonance (ESR) spectrum of Mn(2+) ion in solution. It was found that monomolecular binding constants decreased markedly when reactant concentrations were increased from .00001 to .001 M. The apparent decrease in binding constant would be removed if 2 moles of ATP were assumed to be complexed to 1 mole of Mn(2+) ion. The amount of Mn(2+) which should be liberated during the course of an ATPase reaction was calculated on the basis of the difference in binding constant between Mn-ATP and Mn-ADP. Dog kidney microsomes which contained demonstrable ATPase activity did not release Mn(2+) from Mn-ATP, but instead trapped Mn(2+) in a form not giving the usual Mn(2+) ESR signal even under conditions allowing complete dephosphorylation of ATP to adenosine. These results support the hypothesis that an ATP-dependent mechanism for trapping divalent metals is present in kidney microsomes. This system may be of importance in the renal metabolism of divalent metals. (Author)