Sorption of Heavy Metal Cations by Corn Mitochondria and the Effects on Electron and Energy Transfer Reactions

The passive sorption of Pb +2 , Cd +2 , Zn +2 , Co +2 , Ni +2 , and Mn +2 by isolated corn mitochondria was determined, and, except for Pb +2 , the maximum sorption for each cation was about 58 nmol per milligram of protein. Sorption of Pb +2 was apparently ten times greater, but precipitation may have been the cause of this larger value. The effects of Pb +2 , Cd +2 , Zn +2 , Co +2 , and Ni +2 on acceptorless rates of electron transport for three substrates were determined. Greater than 50% inhibitions of oxidation were observed for succinate after additions of >0.1 m M Cd +2 , Zn +2 , or Pb +2 : for NADH after additions of >0.5 m M Cd +2 or Zn +2 ; and for malate + pyruvate after additions of >0.1 m M Cd +2 . Some inhibition of the rate of substrate oxidation was observed for most cations at higher concentrations. Coupling, as measured by ADP/O ratios, was inhibited at lowest concentrations by Cd +2 or Zn +2 and at higher concentrations by Co +2 or Ni +2 . Substantial swelling of mitochondria oxidizing succinate was observed following additions of O.1 m M Cd +2 or Pb +2 , Correlations are drawn between the effects of Pb +2 , Cd +2 , Zn +2 , Co +2 , and Ni +2 and their sorption to mitochondrial membranes.