ARSENIC BINDING-PROTEINS OF MAMMALIAN SYSTEMS .1. ISOLATION OF 3 ARSENITE-BINDING PROTEINS OF RABBIT LIVER

It is well known that arsenite/arsenate (As3+/As5+) administered to ra bbits is bound initially to cellular proteins of the liver before meth ylated arsenic metabolites appear in urine. This protein binding may d ecrease the in situ toxicity of inorganic arsenic by decreasing its me tabolic availability until it is methylated enzymatically. We have inv estigated the binding of As3+ and As5+ to the cytosolic proteins of ra bbit liver. The results indicate that when cytosolic proteins are incu bated with inorganic arsenic, the amount of As3+ bound is 13 times gre ater than that for As5+. Arsenite-specific binding sites on cytosolic proteins were determined to be 67% of the total (specific and non-spec ific) number of possible binding sites. Ammonium sulfate fractionation , non-denaturing PAGE and gel filtration chromatography indicate that three liver proteins with molecular weights of 100 kDa, 450 kDa and > 2000 kDa strongly bind arsenite. The radioactive profiles after gel fi ltration chromatography of liver cytosolic proteins are very similar w hether As3+ binding occurs in vitro or in vivo. Thus, the in vitro mod el appears to be valid for further study of these arsenite-binding pro teins.